Clearblue Ovulation Calculator Guide

How Clearblue Ovulation Tests Work

Clearblue ovulation tests work by detecting hormones in your urine that indicate ovulation is approaching. Understanding this science helps you use the tests more effectively and interpret results with confidence. For a broader look at how ovulation fits into your menstrual cycle, see our guide on the menstrual cycle and ovulation explained.

The LH Surge

The primary hormone detected by Clearblue tests is luteinizing hormone (LH). Throughout most of your cycle, LH levels remain relatively low. However, about 24-36 hours before ovulation, your pituitary gland releases a surge of LH that triggers the release of the egg from the ovary. According to research published on PubMed, this LH surge is the most reliable hormonal predictor of impending ovulation.

By detecting this LH surge, Clearblue tests identify the two most fertile days of your cycle -- the day before ovulation and the day of ovulation itself. Having intercourse on these days gives you the best chance of conception. For more on recognizing when ovulation is happening, check out our signs of ovulation guide.

Estrogen Detection (Advanced Products)

Some Clearblue products, like the Advanced Digital Ovulation Test, also detect rising estrogen levels. Estrogen begins to rise several days before the LH surge, creating a wider fertile window. This is similar to the biological changes described in our cervical mucus and fertility guide -- rising estrogen is what transforms cervical mucus into its fertile, egg-white consistency.

• Rising estrogen: Indicates "High Fertility" days in the days leading up to the LH surge
• LH surge: Indicates "Peak Fertility" days -- the most fertile time

This dual-hormone detection can identify up to 4 fertile days, giving you more opportunities to conceive each cycle. The American College of Obstetricians and Gynecologists (ACOG) recognizes hormone-based ovulation prediction as a reliable method for timing conception.

Why Detection Timing Matters

Sperm can survive in the female reproductive tract for up to 5 days, but the egg only survives for 12-24 hours after ovulation. This means the best time for conception is actually before ovulation occurs, when sperm can be waiting for the egg to be released. The LH surge gives you advance notice that ovulation is imminent. As the Mayo Clinic explains, timing intercourse in the days leading up to ovulation maximizes your probability of conception.

Clearblue Product Comparison

Clearblue offers several ovulation testing options, each designed for different needs and budgets. Understanding the differences helps you choose the right product. You can also compare these with other options in our comprehensive OPK guide.

Basic Digital Ovulation Test

The simplest Clearblue option detects only the LH surge, displaying a clear smiley face when your two most fertile days have arrived. This is a straightforward, budget-friendly choice if you just want to know your peak days. As Clearblue's official product page notes, it eliminates the guesswork of interpreting lines on traditional OPKs.

Advanced Digital Ovulation Test

By detecting both estrogen and LH, this test identifies more fertile days. Results display as:

• Empty circle: Low fertility
• Flashing smiley: High fertility (rising estrogen)
• Solid smiley: Peak fertility (LH surge detected)

The flashing smiley typically appears 1-2 days before the solid smiley, giving you more time to plan intercourse. This added window aligns with research from Wilcox et al. (1999) showing that conception probability peaks in the 2-3 days before ovulation.

Connected Ovulation Test System

This modern option syncs with the Clearblue app on your smartphone. It provides the same detection as the Advanced test but stores your cycle data, tracks patterns over time, and provides personalized insights. The app can also integrate with Apple Health. If you're already using a fertility tracker app, the Connected system can complement your existing tracking routine.

Clearblue Fertility Monitor

The most comprehensive option, this touchscreen monitor tracks your entire cycle and stores data from multiple cycles. It can identify up to 6 fertile days and is particularly useful for those who want detailed cycle analysis or have irregular cycles.

When to Start Testing

Starting to test at the right time is essential for not missing your LH surge. Start too late, and you might miss your fertile window entirely. Start too early, and you'll use more test sticks than necessary.

Calculating Your Start Day

The day you should start testing depends on your typical cycle length. Count the first day of your period as Day 1, then begin testing according to this comprehensive schedule:

Note: Expected ovulation is estimated by subtracting 14 days (average luteal phase) from cycle length. Individual variation is common. Use our ovulation calculator for a more personalized estimate.

If Your Cycles Are Irregular

For irregular cycles, base your testing start on your shortest cycle in the past 6 months. For example, if your cycles range from 26 to 35 days, use the 26-day schedule and start on Day 9. You may need to test for more days, so consider getting a larger pack of test sticks.

Our ovulation calculator can help you estimate your testing start date based on your cycle information. The ACOG defines irregular cycles as those varying by more than 7-9 days in length.

What Time of Day to Test

For best results:

• Basic Digital Test: Test with your first morning urine, which has the highest concentration of LH.
• Advanced Digital Test: Use first morning urine. The estrogen detection works best with the first urine of the day.
• Consistency: Test at approximately the same time each day (within a 4-hour window).
• Avoid excess fluids: Don't drink large amounts of liquid in the 2 hours before testing, as this can dilute your urine.

How to Use Clearblue Tests

Proper technique ensures accurate results. While each Clearblue product has specific instructions, here are general guidelines that apply across the product line.

Step-by-Step Instructions

1. Remove the test stick from its foil wrapper and remove the cap to expose the absorbent tip.
2. Insert the test stick into the test holder until it clicks (for digital products).
3. Point the absorbent tip downward and either hold it in your urine stream for 5-7 seconds or dip it in a collected urine sample for 15 seconds.
4. Replace the cap and lay the test flat or hold it pointed downward.
5. Wait for the result to appear (usually within 3-5 minutes). A flashing test symbol means the test is working.
6. Read your result within 8 minutes of the symbol stopping flashing.

Tips for Accurate Results

• Don't use the test if the foil wrapper is damaged or the expiration date has passed
• Ensure the absorbent tip is thoroughly saturated
• Don't tilt the test upward while waiting for results
• For the Advanced test, use only with the holder that came in the same pack (it calibrates to your baseline)
• Eject and dispose of used test sticks; they cannot be reread later

Special Considerations

Certain factors can affect Clearblue test results. The FDA advises users to consider these when interpreting results:

• Fertility medications: Clomid, injectable gonadotropins, and some other medications can cause false results. Consult your doctor.
• Recently pregnant: HCG from a recent pregnancy can affect results. Wait for 2 normal cycles before testing.
• PCOS: Polycystic ovary syndrome can cause elevated LH levels that may trigger false positives. See our PCOS section below for detailed guidance.
• Perimenopause: Irregular hormone levels may affect accuracy.

Reading and Interpreting Results

Understanding what your Clearblue results mean helps you take action at the right time. Below is a comprehensive interpreting guide for all Clearblue products.

Basic Digital Test Results

• Empty circle: LH surge not detected. Continue testing tomorrow.
• Smiley face: LH surge detected! You're at peak fertility. Your 2 most fertile days are today and tomorrow.

Advanced Digital Test Results

• Empty circle: Low fertility. LH and estrogen levels are baseline. Continue testing tomorrow.
• Flashing smiley face: High fertility. Estrogen is rising, indicating you're approaching ovulation. This is a good time to have intercourse. Continue testing daily.
• Solid smiley face: Peak fertility. LH surge detected. You're at your most fertile for the next 48 hours. No need to continue testing this cycle.

What If You Never Get a Peak?

If you test for 10+ days without seeing a peak result, you may have:

• Started testing too late in your cycle
• Had an anovulatory cycle (no ovulation)
• Missed a short LH surge
• An underlying hormonal issue

Try again next cycle, starting testing earlier. If this happens repeatedly, consult a healthcare provider. Our guide on when to see a fertility specialist can help you decide if it's time for professional evaluation.

What If You Get Many High Days?

With the Advanced test, some women see many days of "High" fertility before getting a Peak. This can happen if:

• Your estrogen rises gradually
• You have longer cycles
• Ovulation is slightly delayed that month

Continue testing daily until you see Peak. Having intercourse during High fertility days is still beneficial. According to Healthline, conception is possible during the entire High fertility window, not just at Peak.

Timing Intercourse for Conception

Knowing your fertile days is only half the equation -- you also need to time intercourse effectively. For a deeper dive into optimal timing strategies, see our dedicated fertile window guide.

When to Have Intercourse

• High fertility days: Have intercourse at least every other day when you see the flashing smiley.
• Peak fertility days: Have intercourse on the day you see the solid smiley and the following day.

Sperm can survive for up to 5 days in the reproductive tract, so having intercourse before ovulation means sperm will be ready and waiting when the egg is released.

Optimal Frequency

Research suggests that having intercourse every 1-2 days during your fertile window maximizes your chances. Daily intercourse is fine if desired, but every other day is sufficient and may be less stressful. As the American Society for Reproductive Medicine (2017) notes, there's no need to "save up" sperm -- frequent ejaculation doesn't significantly decrease sperm quality in men with normal sperm counts.

After Peak Fertility

Once you've seen the Peak result (solid smiley), ovulation will likely occur within 24-36 hours. Continue having intercourse for the next day or two to maximize your chances. After that, the fertile window has closed for this cycle.

Combining With Other Methods

For best results, combine Clearblue testing with other fertility awareness methods:

• Use our ovulation calculator to estimate your fertile window before you start testing
• Observe cervical mucus changes (egg-white mucus indicates fertility)
• Track basal body temperature to confirm ovulation occurred
• Use a fertility tracker app to record all your data in one place

Pairing Clearblue with Our Free Ovulation Calculator

While Clearblue tests give you real-time hormone data, our free ovulation calculator provides cycle-based predictions that help you plan your testing strategy. Using both tools together creates a powerful, multi-layered approach to fertility tracking.

How to Use Both Tools Together

Here's a step-by-step approach for combining digital ovulation tests with calendar-based predictions:

1. Start with the calculator: Enter your last period date and average cycle length into our ovulation calculator. Note the predicted ovulation date and fertile window.
2. Plan your testing window: Begin Clearblue testing 3-4 days before the calculator's earliest fertile day prediction. This ensures you won't miss an early surge.
3. Test daily: Use your Clearblue test each morning during the predicted fertile window. Record each result alongside the calculator's predictions.
4. Compare and learn: After each cycle, compare when Clearblue detected your surge versus when the calculator predicted it. Over time, this reveals your personal pattern.
5. Refine predictions: If your actual ovulation consistently differs from the calculator's prediction, adjust your cycle length input or note your typical offset.

Entering Clearblue Results into Calendar Tracking

Keeping a record of your Clearblue results alongside calendar predictions helps you build a comprehensive fertility picture:

• Day + Result: Record the cycle day and whether you got Low, High, or Peak
• Calculator comparison: Note whether the calculator predicted "fertile" or "non-fertile" for that same day
• Pattern recognition: After 3+ cycles, you'll see how your actual hormone patterns compare to algorithmic predictions
• Intercourse timing: Log when intercourse occurred relative to both Clearblue results and calculator predictions

Many women find that the calculator's predicted ovulation date is accurate within 1-2 days, but individual cycles can vary. Clearblue results confirm the exact timing for each specific cycle, which is especially valuable if you have irregular periods.

Comparing Predictions Over Multiple Cycles

Research published in Current Medical Research and Opinion found that calendar-based apps can predict ovulation within a few days for regular cycles, but real-time hormone testing significantly improves accuracy. The combination approach works because:

• The calculator helps you plan ahead -- scheduling testing, appointments, and travel around your expected fertile days
• Clearblue tests give you real-time confirmation -- the actual hormone signal that ovulation is imminent
• Together, they help you save money -- start testing only when the calculator says you're getting close, rather than testing from Day 5 onward

Cost Analysis: Is Clearblue Worth the Premium?

Clearblue products carry a significant price premium over generic OPK strips. Understanding the real cost per cycle helps you decide where to invest your fertility tracking budget.

Cost Per Cycle Breakdown

Here's what you can expect to spend per cycle with each option, assuming you need 5-7 tests to detect your surge:

• Generic strip OPKs: $1-$3 per cycle (at $0.20-$0.50 per strip). Bulk packs of 50-100 strips offer the best value.
• Clearblue Digital: $11-$18 per cycle (at $2.00-$3.50 per test). A 20-pack covers 2-3 cycles.
• Clearblue Advanced Digital: $18-$25 per cycle (at $3.50-$5.00 per test). Higher cost but identifies more fertile days.
• Clearblue Connected: $20-$28 per cycle (starter kit includes 25 tests; refill sticks cost $35-$50 for 20).
• Clearblue Fertility Monitor: $30-$45 per cycle for sticks, plus the one-time monitor cost of $100-$150. Gets more cost-effective over time.

When the Premium Is Justified

Clearblue's higher cost is worth it in several situations:

• You struggle with line interpretation: If you've found generic strips confusing or stressful, the clear digital display removes all guesswork
• You want estrogen tracking: The Advanced and Connected tests identify 2+ more fertile days per cycle -- information generic strips simply cannot provide
• You have limited time: Quick, unambiguous results save time and reduce the anxiety of uncertain readings
• You're over 35: When time is a factor, the wider fertile window from dual-hormone detection helps maximize every cycle
• First-time OPK users: Starting with a user-friendly system builds confidence in ovulation tracking

When to Save Money with Generic Strips

Generic OPK strips are the better value when:

• You're comfortable reading lines: With practice, comparing test-to-control line darkness becomes second nature
• You want to test twice daily: At $0.20-$0.50 per strip, testing morning and evening is affordable -- and helps catch short LH surges
• You're tracking long-term: If you're monitoring cycles for many months, the cost savings add up significantly
• You combine with other methods: If you're also using BBT tracking and cervical mucus observation, basic LH confirmation may be all you need

Refill Costs to Consider

Be aware that ongoing costs differ from the initial purchase:

• Clearblue Digital: Refill packs of 20 sticks run $30-$40. The holder from your initial pack is reusable.
• Clearblue Advanced: Refill packs of 20 sticks cost $40-$55. You must use the holder from the same cycle (it calibrates to your baseline).
• Clearblue Connected: Refill packs of 20 sticks cost $35-$50. The Bluetooth holder is reusable.
• Fertility Monitor: Test stick packs (30 sticks) cost $30-$45. The monitor itself lasts for years.

Over 6 months of trying to conceive, total costs range from approximately $12-$18 (generic strips) to $120-$180 (Clearblue Advanced) to $250+ (Fertility Monitor including hardware). As WebMD notes, the choice often comes down to personal preference and how much clarity you want from your results.

Clearblue for PCOS and Irregular Cycles

Polycystic ovary syndrome (PCOS) affects approximately 6-12% of women of reproductive age, according to the CDC. If you have PCOS or significantly irregular cycles, using Clearblue tests requires special consideration because the hormonal landscape differs from what these tests are designed to detect.

The Challenge: High Baseline LH

Many women with PCOS have chronically elevated LH levels -- sometimes 2-3 times higher than normal baseline. This creates a fundamental problem for OPKs:

• False positives: Your baseline LH may already exceed the test's threshold, causing the test to show positive results even when you're not about to ovulate
• No detectable surge: If your LH is already high, the pre-ovulatory surge may not appear as distinct, making it harder for the test to differentiate between baseline and surge levels
• Multiple surges: PCOS can cause multiple attempted ovulations throughout a cycle, each producing a small LH rise that may or may not be detected

When Clearblue Advanced Works Better for PCOS

The Clearblue Advanced Digital test may be a better choice for PCOS patients than the basic Digital test because:

• Estrogen tracking provides additional data: Rising estrogen indicates follicular development, which is a more reliable indicator than LH alone in PCOS
• Baseline calibration: The Advanced test calibrates to your personal hormone levels at the start of each cycle, which can partially account for elevated LH
• High fertility readings: Even if Peak readings are unreliable, High readings from estrogen can still indicate that your body is attempting to ovulate

Research published in Fertility and Sterility has shown that dual-hormone OPKs provide more useful information for women with ovulatory dysfunction than LH-only tests.

When to Avoid Digital OPKs

In some cases, Clearblue tests (or any digital OPK) may not be the best choice:

• Severely elevated LH (>2x normal): If your baseline LH is very high, no OPK can reliably distinguish a surge from your normal levels
• Very long cycles (>45 days): You would need too many test sticks, making the cost prohibitive. Consider ultrasound monitoring instead.
• On metformin or letrozole: Some PCOS medications change your hormonal patterns in ways that may confuse OPK algorithms. Discuss with your doctor.
• Anovulatory for 3+ months: If you haven't had a period in over 3 months, ovulation tests aren't the right starting point. See a fertility specialist first.

Alternative Approaches for PCOS

If Clearblue tests aren't giving you reliable results, consider these alternatives:

• BBT tracking: Basal body temperature confirms ovulation after the fact and isn't affected by baseline LH levels. It works well for PCOS because the temperature shift is hormone-independent.
• Cervical mucus monitoring: Egg-white cervical mucus is a reliable indicator of rising estrogen and approaching ovulation, even with PCOS.
• Quantitative LH testing: Semi-quantitative OPK strips (like Premom or Easy@Home with app readings) show your actual LH level rather than just positive/negative. This helps you see the surge pattern even with elevated baseline.
• Ultrasound monitoring: Your doctor can track follicle development via ultrasound, providing definitive confirmation of ovulation timing.
• Progesterone testing: A mid-luteal phase blood test (about 7 days after suspected ovulation) can confirm whether ovulation actually occurred.

Clearblue Digital vs. Advanced Digital: Detailed Comparison

Choosing between the Clearblue Digital (Smiley) and the Advanced Digital is one of the most common decisions for women starting with ovulation predictor kits. The table below breaks down every meaningful difference so you can pick the right test for your situation.

Understanding Clearblue Smiley Results

The smiley face system is Clearblue's signature feature, replacing confusing test lines with clear symbols. Here is a complete reference for every possible display you may see when using the Clearblue Digital or Advanced Digital ovulation test.

For women using the standard Digital test (not Advanced), only two results are possible: the empty circle (no surge) and the solid smiley (LH surge detected). The flashing smiley is exclusive to the Advanced Digital and Connected models because it requires estrogen detection. For more details on reading OPK results generally, see our complete OPK guide.

Troubleshooting Common Clearblue Issues

Even with digital technology, issues can arise. This quick-reference table covers the most common problems users encounter with Clearblue ovulation tests and how to resolve them. If you are experiencing persistent issues, consider combining Clearblue with BBT tracking for more complete fertility data.

If you have tried these solutions and continue to experience problems, our guide on when to see a fertility specialist can help you determine if professional evaluation is warranted.

Troubleshooting Common Issues

No Result Appearing

If the test doesn't display a result:

• Check that the test stick was inserted correctly into the holder
• Ensure enough urine was applied
• Verify the test isn't expired
• Wait the full time for results (don't remove the stick early)

Error Symbol

An error symbol may appear if:

• Too much or too little urine was applied
• The test was moved during processing
• There's a problem with the test stick

Discard the test stick and try again with a new one. If errors persist across multiple sticks, contact Clearblue customer support.

Faint Lines (Non-Digital Tests)

If using non-digital OPKs (other brands), a faint line can be confusing. With Clearblue digital tests, you don't need to interpret line darkness -- the digital display gives you a clear yes/no answer. For tips on reading traditional strip OPKs, see our OPK guide.

Persistent Low Results

If you consistently see Low fertility and never High or Peak:

• Start testing earlier in your cycle
• Test twice daily (morning and evening) as some women have short LH surges
• Consult your doctor if this persists across multiple cycles

Switching From One Test Type to Another

If you change Clearblue products mid-cycle, you may not get accurate results because the Advanced test needs to establish your personal baseline at the start of your cycle. Wait until a new cycle to switch products.

Clearblue vs. Other OPK Brands

While Clearblue dominates the digital OPK market, several other brands offer competitive ovulation predictor kits at different price points and with varying features. The American Society for Reproductive Medicine (ASRM) notes that all properly manufactured LH-detection tests use similar immunoassay technology, meaning the core detection mechanism is comparable across brands. The differences lie in user experience, additional features, sensitivity thresholds, and cost per cycle. Understanding these distinctions can help you choose the best option for your budget and tracking preferences.

Whether you are new to ovulation testing or considering a switch from one brand to another, the following comparison covers the six most widely used OPK brands available in 2026. For a broader overview of how all ovulation predictor kits work, see our complete OPK guide.

As the NHS explains, the fundamental science behind all OPKs is the same -- they detect the LH surge that occurs 24-36 hours before ovulation. The choice between brands comes down to whether you prefer the convenience of a digital readout (Clearblue, First Response) or the affordability of strip tests that let you test multiple times per day without worrying about cost (Easy@Home, Wondfo). For women with shorter LH surges or lower baseline LH, the more sensitive 25 mIU/mL strips may catch surges that the 40 mIU/mL Clearblue Digital would miss.

Many experienced users adopt a hybrid approach: using inexpensive strips for daily monitoring throughout their fertile window, then confirming with a Clearblue Digital test when the strips begin to darken. This strategy keeps costs manageable while providing the certainty of a digital readout at the critical moment. If you are also tracking basal body temperature or cervical mucus, you already have additional confirmation methods that reduce the need for premium testing.

Interpreting Your Clearblue Results

Understanding what each Clearblue result means -- and what action to take -- is essential for maximizing your chances of conception. The Advanced Digital test provides three distinct fertility levels, each corresponding to specific hormonal changes in your body. The Cleveland Clinic explains that the hormonal cascade leading to ovulation follows a predictable sequence, and Clearblue tests are designed to map directly onto this progression.

The timeline below shows the typical testing sequence over a cycle, from the first Low reading through Peak fertility, along with the recommended actions at each stage. Keep in mind that individual cycles can vary, and the number of days at each level is approximate.

Result-to-Action Quick Reference

One common misconception is that you should only have intercourse on the Peak day. In reality, the Johns Hopkins Medicine fertility resource confirms that sperm can survive for up to 5 days in the female reproductive tract, so intercourse during High fertility days (before Peak) is also highly effective. The ideal pattern is to have intercourse every 1-2 days from the first High reading through the day after Peak. This ensures that viable sperm are present in the fallopian tubes when the egg is released.

Troubleshooting Common OPK Issues

Even with clear digital readouts, Clearblue users occasionally encounter confusing or unexpected results. Most issues have straightforward explanations and solutions. The ASRM notes that user error -- not test failure -- accounts for the vast majority of unexpected OPK results. Understanding the most common problems and their solutions can save you from unnecessary frustration and wasted test sticks.

The table below covers the most frequently reported issues with Clearblue and other OPK tests, along with their likely causes and recommended solutions. If you experience persistent problems across multiple cycles, it may be worth discussing your results with a healthcare provider or considering whether you should see a fertility specialist.

The Cleveland Clinic emphasizes that OPKs are designed to be used alongside other signs of ovulation, not as a standalone diagnostic tool. If your Clearblue results do not align with what your body is telling you -- for example, you are seeing fertile cervical mucus but no High or Peak readings -- trust the combination of signals rather than any single data point. Use our ovulation calculator to cross-reference your expected fertile window with your test results.

Related Reading

Explore our complete library of fertility and reproductive health resources:

• Ovulation Calculator -- Free tool to estimate your fertile window
• About Us -- Learn about our mission and methodology
• The Menstrual Cycle and Ovulation Explained
• Menstrual Cycle Phases Explained
• Signs of Ovulation
• How Many Days After Your Period Do You Ovulate?
• How Long After Ovulation Is Your Period?
• The Fertile Window: When to Conceive
• Basal Body Temperature and Ovulation
• Cervical Mucus and Fertility
• Complete Guide to Ovulation Predictor Kits (OPKs)
• Best Fertility Tracker Apps Compared
• Irregular Periods and Ovulation
• Ovulation With Irregular Periods
• How Due Dates Are Calculated
• Due Date Calculator From Ovulation
• When to See a Fertility Specialist

Frequently Asked Questions

Helpful Resources

For further reading on ovulation testing, fertility, and reproductive health, explore these trusted resources:

External Resources

• Clearblue Official Ovulation Test Information -- Product details, instructions, and FAQs directly from the manufacturer.
• ACOG: Evaluating Infertility -- Evidence-based guidance from the American College of Obstetricians and Gynecologists.
• Mayo Clinic: How to Get Pregnant -- Comprehensive overview of conception timing and strategies.
• FDA: Ovulation Urine Tests -- Regulatory information on how home ovulation tests are classified and evaluated.
• ASRM: Infertility Topics -- Educational resources from the American Society for Reproductive Medicine.
• CDC: PCOS Information -- Government health information on polycystic ovary syndrome.
• RESOLVE: Understanding Infertility -- The National Infertility Association's patient-focused resources.
• Healthline: Ovulation Kits Guide -- Accessible overview of OPK types and how to use them.

Related Articles on Our Site

• Complete Guide to Ovulation Predictor Kits (OPKs) -- In-depth comparison of all OPK brands and types, including how to read line-based strips.
• The Menstrual Cycle and Ovulation Explained -- Understand the full hormonal cycle that Clearblue tests are designed to detect.
• Signs of Ovulation -- Learn to recognize physical symptoms of ovulation that complement your Clearblue results.
• How Many Days After Your Period Do You Ovulate? -- Understand the timing of ovulation relative to your menstrual period.

Sources

• Johnson, S., Marriott, L., & Zinaman, M. (2018). Can apps and calendar methods predict ovulation with accuracy? Current Medical Research and Opinion, 34(9), 1587-1594. PubMed
• Clearblue Official Product Information and Instructions for Use. Clearblue.com
• Stanford, J. B., White, G. L., & Hatasaka, H. (2002). Timing intercourse to achieve pregnancy: current evidence. Obstetrics & Gynecology, 100(6), 1333-1341. PubMed
• American Society for Reproductive Medicine. (2017). Optimizing natural fertility: a committee opinion. Fertility and Sterility, 107(1), 52-58. PubMed
• Wilcox, A. J., Dunson, D., & Baird, D. D. (1999). The timing of the "fertile window" in the menstrual cycle. BMJ, 321(7271), 1259-1262. PubMed
• American College of Obstetricians and Gynecologists (ACOG). Evaluating Infertility. ACOG.org
• Mayo Clinic. How to get pregnant. MayoClinic.org
• U.S. Food and Drug Administration. Ovulation (Urine Test). FDA.gov
• Centers for Disease Control and Prevention. PCOS (Polycystic Ovary Syndrome) and Diabetes. CDC.gov