Ovulation & fertile window calculator

Ovulation on a 35-Day Cycle

On a 35-day cycle with a typical 14-day luteal phase, ovulation falls on about day 21 of the cycle — counted backwards from the next period, not forwards from the last one. Your fertile window is the six days ending on that day. Use the calculator for your own dates, or look them up in the table below.

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Estimated ovulation
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Fertile window
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6 days: the 5 days before ovulation, plus ovulation day
Next period expected
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If you conceive this cycle
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Estimated due date (ovulation + 266 days)

Your fertile days, day by day

Per-day figures are the published estimates of Wilcox, Weinberg & Baird (New England Journal of Medicine, 1995), from 221 women whose ovulation day was confirmed by hormone testing: roughly 10% five days before ovulation, 16% four days before, 14% three days before, 27% two days before, 31% one day before and 33% on ovulation day itself — and effectively 0% the day after. They are population averages from a modest sample, not a personal prediction.

This cycle on a calendar

PeriodFertile windowOvulation day

Your next cycles at a glance

Each later cycle assumes the same average length. Real cycles drift by a few days, so treat dates further out as rougher estimates.

Already pregnant, or checking a date? Pregnant? Calculate your due date →
DueDateCalc works out your due date, week-by-week timeline and milestones.

35-day cycle quick facts

Ovulation day

About day 21 of the cycle (cycle length − 14). The follicular phase — period to ovulation — runs about 21 days, which is where a 35-day cycle gets most of its difference in length versus a 28-day cycle.

Fertile window

Days 16–21 of the cycle: the five days before ovulation plus ovulation day itself, when sperm survival (up to 5 days) overlaps the egg's short life.

Best odds

The last two days of the window carry the highest published per-day odds — about 27–31% the two days before ovulation and roughly 33% on ovulation day (Wilcox et al., NEJM 1995).

Lookup table — last period in October 2026

If your last period started on one of these dates and your cycle is 35 days, here are your estimated dates. Every row is generated with the same math as the calculator (ovulation = period + 21 days; due date = ovulation + 266 days).

Last period startedFertile windowOvulationNext period
Oct 1, 2026Oct 17 – Oct 22Oct 22, 2026Nov 5, 2026
Oct 2, 2026Oct 18 – Oct 23Oct 23, 2026Nov 6, 2026
Oct 3, 2026Oct 19 – Oct 24Oct 24, 2026Nov 7, 2026
Oct 4, 2026Oct 20 – Oct 25Oct 25, 2026Nov 8, 2026
Oct 5, 2026Oct 21 – Oct 26Oct 26, 2026Nov 9, 2026
Oct 6, 2026Oct 22 – Oct 27Oct 27, 2026Nov 10, 2026
Oct 7, 2026Oct 23 – Oct 28Oct 28, 2026Nov 11, 2026
Oct 8, 2026Oct 24 – Oct 29Oct 29, 2026Nov 12, 2026
Oct 9, 2026Oct 25 – Oct 30Oct 30, 2026Nov 13, 2026
Oct 10, 2026Oct 26 – Oct 31Oct 31, 2026Nov 14, 2026
Oct 11, 2026Oct 27 – Nov 1Nov 1, 2026Nov 15, 2026
Oct 12, 2026Oct 28 – Nov 2Nov 2, 2026Nov 16, 2026
Oct 13, 2026Oct 29 – Nov 3Nov 3, 2026Nov 17, 2026
Oct 14, 2026Oct 30 – Nov 4Nov 4, 2026Nov 18, 2026
Oct 15, 2026Oct 31 – Nov 5Nov 5, 2026Nov 19, 2026
Oct 16, 2026Nov 1 – Nov 6Nov 6, 2026Nov 20, 2026
Oct 17, 2026Nov 2 – Nov 7Nov 7, 2026Nov 21, 2026
Oct 18, 2026Nov 3 – Nov 8Nov 8, 2026Nov 22, 2026
Oct 19, 2026Nov 4 – Nov 9Nov 9, 2026Nov 23, 2026
Oct 20, 2026Nov 5 – Nov 10Nov 10, 2026Nov 24, 2026
Oct 21, 2026Nov 6 – Nov 11Nov 11, 2026Nov 25, 2026
Oct 22, 2026Nov 7 – Nov 12Nov 12, 2026Nov 26, 2026
Oct 23, 2026Nov 8 – Nov 13Nov 13, 2026Nov 27, 2026
Oct 24, 2026Nov 9 – Nov 14Nov 14, 2026Nov 28, 2026
Oct 25, 2026Nov 10 – Nov 15Nov 15, 2026Nov 29, 2026
Oct 26, 2026Nov 11 – Nov 16Nov 16, 2026Nov 30, 2026
Oct 27, 2026Nov 12 – Nov 17Nov 17, 2026Dec 1, 2026
Oct 28, 2026Nov 13 – Nov 18Nov 18, 2026Dec 2, 2026
Oct 29, 2026Nov 14 – Nov 19Nov 19, 2026Dec 3, 2026
Oct 30, 2026Nov 15 – Nov 20Nov 20, 2026Dec 4, 2026
Oct 31, 2026Nov 16 – Nov 21Nov 21, 2026Dec 5, 2026

For a period that started in a different month, the pattern simply shifts: add 35 days for the next period, and count 21 days after the start for ovulation — or use the calculator above, which does exactly that for any date.

Please read: OvulationCalc is an estimation tool based on calendar averages. It is not medical advice, it cannot confirm that ovulation has happened, and it must not be used as a contraception method — calendar estimates are not reliable birth control. Cycles vary from month to month. If you are trying to conceive, have irregular cycles, or have any health concern, talk to a doctor or midwife.