Ovulation Calculator
Calculate your fertile window and date of ovulation.
Expected ovulation
Sunday, July 19, 2026
Fertile window
Tuesday, July 14, 2026 - Sunday, July 19, 2026
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Ovulation Calculator: Fertile Window from Cycle Length
Estimate ovulation day and a fertile date range from your last period and average cycle length. Enter Last period start date and Average cycle length (days). Ovulation is placed at cycle length minus 14 days after LMP. Fertile window runs five days before ovulation through ovulation day. Awareness tool only. It does not confirm ovulation and is not contraception.
How to use
Example math: 28-day cycle sets ovulation on day 14 after LMP. Fertile window starts five days earlier. Shorter cycles pull ovulation forward; longer cycles push it back. The 14-day luteal phase assumption is fixed, which may not match your body.
Example
LMP 19 May with a 28-day average points to ovulation near 2 June and a fertile window about 28 May through 2 June. Stress, illness, or PCOS can shift real ovulation by several days.
Tips
Average the last three cycle lengths when you can. Pair with the period calculator for next bleed timing. Seek care if cycles are very irregular or you have trouble conceiving over time. Use approved birth control if you are avoiding pregnancy.