Ovulation Calculator
Calendar sketch of ovulation and fertile days from LMP and cycle length — not a fertility clinic workup. Click any i for detail.
Cycle
First day of last period
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LMP
Day 1 of bleeding for your most recent period. |
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Average cycle length (days)
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Cycle
Days from day-1 to next day-1. 28 is common; many people run 24–35. |
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Luteal length (days)
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Luteal
Days from ovulation to next period. Default 14; adjust if you chart a different luteal phase. |
How to use this calculator
- Enter the first day of your last period.
- Set your usual cycle length (and luteal length if you know it).
- Read the estimated ovulation date, fertile window, and next-period sketch.
- Confirm with OPKs, temps, or your clinician when timing matters.
Results explained
Most trackers place ovulation about luteal-length days before the next period. With a 28-day cycle and a 14-day luteal phase that is day 14. Sperm can survive several days, so the fertile window usually starts about five days before ovulation and ends the day after. Irregular cycles, illness, travel, and PCOS can shift timing; this page does not read labs or ultrasound.
Quick reference: cycle sketch
Ovulation day ≈ cycle length − luteal length (often cycle − 14).
| Item | Detail |
|---|---|
| 28-day cycle | Ovulation ~ day 14; fertile ~ days 9–15 |
| 32-day cycle | Ovulation ~ day 18 if luteal stays 14 |
| Short luteal (10d) | Ovulation later than the classic mid-point |
| Best confirmation | LH tests, cervical mucus, or clinician guidance |
Educational only — not contraception advice and not a pregnancy test.
How the estimate is built
ovulation_day = cycle_length − luteal_length; fertile ≈ [ovulation − 5, ovulation + 1]; next_period ≈ LMP + cycle_length.
Example scenario
LMP March 1, 28-day cycle, 14-day luteal → ovulation ~ March 15, fertile ~ March 10–16.
FAQ
Can I use this as birth control?
No. Calendar methods fail often without training and perfect use. Use contraception your clinician recommends if avoiding pregnancy is the goal.
What if my cycles vary by a week?
Use a recent average, or run the tool twice with your shortest and longest cycles to see a wider window. Highly irregular cycles need personalized care, not fixed mid-cycle arithmetic.
Why change luteal length?
If you chart and get a period 10–12 days after ovulation signs, a shorter luteal input moves the estimate later. Leave 14 if you do not chart.
Does spotting count as day 1?
Usually day 1 is the first day of full flow. Follow the definition your clinic or tracking app uses so inputs stay consistent.