Ovulation calculator
When are my fertile days? Enter the first day of your last period and your usual cycle length to see your next fertile windows.
Runs in your browser. Nothing you type leaves this page.
Ovulation
Tuesday 20 October
today
| Fertile window | Ovulation | Next period |
|---|---|---|
| 15–21 Oct | 20 Oct | 3 Nov |
| 12–18 Nov | 17 Nov | 1 Dec |
| 10–16 Dec | 15 Dec | 29 Dec |
| 7–13 Jan | 12 Jan | 26 Jan |
| 4–10 Feb | 9 Feb | 23 Feb |
| 4–10 Mar | 9 Mar | 23 Mar |
An estimate, not medical advice. Do not use it as birth control.
How it works
Ovulation usually happens 10 to 16 days before the next period, so we count back 14 days from your expected period. Nearly all pregnancies come from sex in the six days that end on ovulation day; we show those six days plus the day after as your fertile window.
Sources: NHS: Fertility in the menstrual cycle , Wilcox et al., NEJM, 1995
Questions
- When am I most fertile?
- On ovulation day and the days just before it.
- What if my cycles are irregular?
- Then the dates will be off. Ovulation tests or basal body temperature give a better signal. Vela hides the fertile window when your logged cycles are too irregular to estimate it honestly.
- Can I use this to avoid pregnancy?
- No. A calendar estimate cannot confirm ovulation. Use a method made for contraception and talk to a clinician.
- Is anything I type saved?
- No. The calculation runs in your browser, and nothing you type is sent or stored.
Let your own cycles do the math
Vela learns your cycle from your own logs and keeps them on your iPhone. No account needed.
More calculators: Period calculator Due date calculator