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SnapCalculations

Ovulation Calculator

Enter the first day of your last period and your usual cycle length to see your fertile window, ovulation day and next period for three cycles.

days
days

Days from ovulation to your next period. 14 is typical; leave it if unsure.

Pick a date, a cycle length of 21–45 days and a luteal phase of 10–16 days.

How it works

  • Ovulation usually happens about 14 days before your next period (the luteal phase), so ovulation = period start + cycle length − 14.
  • The fertile window is the 5 days before ovulation plus ovulation day, because sperm can survive for several days.
  • Your next period is expected one cycle length after the last one began.

Worked examples

A 28-day cycle

If the last period started on 1 January 2026 and cycles are 28 days, when is ovulation?

  1. Ovulation ≈ period start + 28 − 14 days = 15 January.
  2. Fertile window = the 5 days before plus ovulation day: 10–15 January.
  3. Next period ≈ 1 Jan + 28 days.

Answer: Ovulation about 15 January; most fertile 10–15 January; next period about 29 January

Try this example

A 32-day cycle

When is ovulation for a 32-day cycle starting on 5 March 2026?

  1. Ovulation ≈ 5 Mar + 32 − 14 = 18 days later.
  2. Fertile window: 18–23 March.

Answer: Ovulation about 23 March; next period about 6 April

Try this example

Frequently asked questions

Can I use this to avoid pregnancy?

No. Cycles vary, and calendar estimates are not reliable contraception.

What if my cycles are irregular?

Use your average cycle length, but treat the dates as rough. Ovulation tests or tracking basal body temperature can pinpoint ovulation more precisely.

Results are estimates for general information and are not financial, medical or professional advice.