Ovulation calculator
Calculator
The calculator needs JavaScript. The tables below give the same numbers for common cases.
How it is worked out
- Ovulation usually happens about 14 days before the next period starts: start + (cycle length − 14).
- The fertile window is the 5 days before ovulation plus the day itself. Cycles vary; this is an estimate and not contraception or a diagnosis.
| Inputs | Answer |
|---|---|
| First day of your last period: 2026-03-01; Cycle length: 28 | Ovulation is expected around Sunday, March 15, 2026; the fertile window runs from Tuesday, March 10, 2026 to Monday, March 16, 2026. |
| First day of your last period: 2026-03-01; Cycle length: 32 | Ovulation is expected around Thursday, March 19, 2026; the fertile window runs from Saturday, March 14, 2026 to Friday, March 20, 2026. |
| First day of your last period: 2026-03-01; Cycle length: 25 | Ovulation is expected around Thursday, March 12, 2026; the fertile window runs from Saturday, March 7, 2026 to Friday, March 13, 2026. |
How to use it
Ovulation usually happens about 14 days before the next period starts, so it falls near day 14 of a 28-day cycle and later in longer cycles. The fertile window is the five days before ovulation plus the day itself, because sperm can survive for several days.
Cycles vary from month to month, so this is an estimate. It is not contraception and not a diagnosis; irregular cycles are best discussed with a healthcare provider. This is general information and an estimate, not medical advice; talk to a healthcare professional about your own situation.
Frequently asked questions
When do I ovulate?
About 14 days before your next period.
How long is the fertile window?
About six days: the five days before ovulation and ovulation day.
Can I use this as birth control?
No; it is an estimate and not reliable contraception.
Method: standard arithmetic shown step by step; no outside data is used. Checked 2026-11-12.
About · How we verify this · Editorial policy · Corrections
General information only. Results are plain arithmetic on the numbers you enter; check anything important (money, health, school work) against your own records or the official source.