FertileWindow

Ovulation Calculator

From the first day of your last period and your typical cycle length — your estimated ovulation day and 6-day fertile window.

First day of last period (LMP)

Cycle length (days)

Ovulation and fertile window by cycle length

Ovulation happens about 14 days before the next period, so a longer cycle pushes it later. Rows below all start from a last period on 1 March 2026.

Cycle length	Fertile window opens	Ovulation	Next period
26 days	8 March	13 March	27 March
28 days	10 March	15 March	29 March
30 days	12 March	17 March	31 March
32 days	14 March	19 March	2 April
35 days	17 March	22 March	5 April

Sperm survive up to five days, which is why the fertile window opens before ovulation. Cycle length varies month to month, so this is a prediction rather than a schedule. General wellness information only, not medical advice. Discuss any health decision with a qualified clinician.

How it's estimated

Ovulation usually happens ~14 days before the next period starts (not after the last one). The fertile window covers the 5 days before ovulation plus the day of, since sperm survive ~5 days.

Confirming ovulation

Calendar predictions are estimates. To confirm ovulation: track basal body temperature (rises 0.3–0.5°C after ovulation), use ovulation predictor kits (detect the LH surge 24–36 hours before), or monitor cervical mucus changes (egg-white consistency around ovulation).

Frequently asked questions

When do I ovulate?

Typically 14 days before your next expected period. For a 28-day cycle: around day 14. For a 32-day cycle: around day 18. For a 25-day cycle: around day 11. The 14-day count is backward from the next period, not forward from the last one — this is a common misconception.

How many days can you get pregnant per cycle?

About 6 days: the 5 days before ovulation plus the day of ovulation. Sperm can survive up to 5 days in the reproductive tract, but the egg only lives 12–24 hours after release. The most fertile days are the 2–3 days immediately before and including ovulation day.

Why is my cycle irregular?

Cycle length varies naturally by 1–5 days. Factors causing more variation: stress, weight changes, exercise intensity, hormonal conditions (PCOS), thyroid disorders, perimenopause, and recent hormonal contraceptive use. Cycles consistently shorter than 21 or longer than 35 days warrant a conversation with a healthcare provider.