Ovulation calculator
Estimate your ovulation date, fertile window and next period.
How it works
Ovulation happens on average 14 days before the next period. The fertile window runs from 5 days before to 1 day after ovulation. Estimate only: not a contraception method.
Results are for guidance only and do not replace professional advice.
Worked example
With the default values:
- First day of your last period31 October 2026
- Average cycle length (days)28
you get:
- Estimated ovulationSaturday, 14 November 2026
- Fertile windowMon 9 November → Sun 15 November
- Next periodSaturday, 28 November 2026
- Following cycle: ovulationSat 12 December
Frequently asked questions
How does the “Ovulation calculator” tool work?
Ovulation happens on average 14 days before the next period. The fertile window runs from 5 days before to 1 day after ovulation. Estimate only: not a contraception method.
What do I need to enter?
Just fill in: first day of your last period, average cycle length. The result updates as you type.
Can you give an example?
First day of your last period: 31 October 2026; Average cycle length (days): 28 → Estimated ovulation: Saturday, 14 November 2026; Fertile window: Mon 9 November → Sun 15 November.
Is this calculator free, and is my data private?
Yes. HOD Calc is completely free with no sign-up. The calculation runs in your browser: nothing you type is sent or stored.