Fertile Window Calculator: Find Your Most Fertile Days
Enter your last period and cycle length to see your fertile window, the peak days, and the windows for your next 6 cycles.
- Nothing you type is stored
- Free
- No signup
Fertile window starts
Fri, 13 Nov 2026
- Fertile window ends
- Thu, 19 Nov 2026
- Peak days start
- Mon, 16 Nov 2026
- Estimated ovulation
- Wed, 18 Nov 2026
- Next period expected
- Wed, 2 Dec 2026
An estimate for general information, not medical advice. Calendar dates are not a reliable method of birth control.
Peak days are the 2 days before ovulation and ovulation day.
Next 6 cycles
| Period starts | Fertile from | Fertile to | Ovulation |
|---|---|---|---|
| Wed, 4 Nov 2026 | Fri, 13 Nov 2026 | Thu, 19 Nov 2026 | Wed, 18 Nov 2026 |
| Wed, 2 Dec 2026 | Fri, 11 Dec 2026 | Thu, 17 Dec 2026 | Wed, 16 Dec 2026 |
| Wed, 30 Dec 2026 | Fri, 8 Jan 2027 | Thu, 14 Jan 2027 | Wed, 13 Jan 2027 |
| Wed, 27 Jan 2027 | Fri, 5 Feb 2027 | Thu, 11 Feb 2027 | Wed, 10 Feb 2027 |
| Wed, 24 Feb 2027 | Fri, 5 Mar 2027 | Thu, 11 Mar 2027 | Wed, 10 Mar 2027 |
| Wed, 24 Mar 2027 | Fri, 2 Apr 2027 | Thu, 8 Apr 2027 | Wed, 7 Apr 2027 |
How to use
- Enter the first day of your last period and your cycle length.
- If your cycles vary, add your shortest and longest cycle under More options.
- See your fertile window, peak days and future windows.
Good to know
The fertile window covers about 6–7 days: the 5 days before ovulation, ovulation day and the day after (Wilcox et al., NEJM 1995). The two days before ovulation and ovulation day itself give the highest chance of pregnancy.
If your cycles vary, the window is widened: it starts 19 days before the end of your shortest cycle and ends 13 days before the end of your longest. This is similar to the classic calendar method and makes the window longer but safer to plan around.
Calendar estimates can be off by several days, especially with PCOS, thyroid problems, after stopping the pill or while breastfeeding. Ovulation test kits are more precise. This tool is to help you plan, not to prevent pregnancy.
Questions
How many days is the fertile window?
About 6 days ending on ovulation day, plus the day after. Peak fertility is the 2 days before ovulation and ovulation day.
Can I get pregnant outside the fertile window?
It is unlikely but possible, because ovulation can come earlier or later than expected.
What if my periods are irregular?
Enter your shortest and longest cycles. The window will be wider to cover the uncertainty.
Is the fertile window safe for avoiding pregnancy?
No. Do not rely on calendar dates for contraception.
Is my data saved?
No. Your dates stay on your device; nothing is stored or sent.