How is ovulation calculated?
Ovulation happens about 14 days before your next period, so subtract 14 from your cycle length: day 14 of a 28-day cycle, day 18 of a 32-day cycle.
Sperm can live for up to 5 days, so the fertile window starts 5 days before ovulation and ends the day after it.
The phase after ovulation (luteal phase) lasts 12–14 days for most women; if you know yours from temperature charting or ovulation tests, enter 10–16. The calculator also shows how many days past ovulation (DPO) you are today and your implantation window.
Ovulation day by cycle length
| Cycle | Ovulation | Fertile window |
|---|---|---|
| 21 | day 7 | day 2 – day 8 |
| 24 | day 10 | day 5 – day 11 |
| 26 | day 12 | day 7 – day 13 |
| 28 | day 14 | day 9 – day 15 |
| 30 | day 16 | day 11 – day 17 |
| 32 | day 18 | day 13 – day 19 |
| 35 | day 21 | day 16 – day 22 |
Frequently asked questions
How many days after my period do I ovulate?
In a regular 28-day cycle, around day 14 counted from the first day of your period. In longer cycles ovulation comes later: cycle length minus 14.
How long is the fertile window?
About 6 days: the 5 days before ovulation and ovulation day, plus the following day. The chance of pregnancy is highest 1–2 days before ovulation.
How many days past ovulation should I test?
For the most reliable result, test on the day your period is due or later, which is about 14 days past ovulation.
Does this work with irregular periods?
The calendar method is an estimate for regular cycles. If your cycle length changes a lot from month to month, ovulation tests or tracking with your doctor are more reliable.