Log the first day of each period and see when your next one is due, your average cycle length and your likely fertile window. Your data stays in your browser.
Loading the tool…
How the tracker works
- Add the first day of your most recent period. Add earlier ones too if you know them.
- The tracker works out the gap between each period (your cycle length) and averages your last six cycles.
- It predicts your next three periods, and estimates ovulation about 14 days before each one.
Until you’ve logged two periods, it uses the cycle length you enter (28 days by default).
Example
| Period started | Cycle length |
|---|---|
| 12 August | – |
| 10 September | 29 days |
| 9 October | 29 days |
| Next period predicted | 7 November |
What’s a normal cycle?
The average menstrual cycle is around 28 days, but anywhere from about 21 to 35 days is common, and it’s normal for it to vary a little from month to month. Ovulation usually happens 10 to 16 days before the next period starts.
See a GP if your periods suddenly change, become very irregular, are very heavy or painful, or stop and you’re not pregnant.
Your privacy
Everything you enter is stored only in this browser on this device. Nothing is uploaded, and there’s no account. Clearing your browser data deletes it.
Frequently asked questions
How do I predict my next period?
Add your last few period start dates. The tracker averages the gaps between them and adds that to your latest period.
What is my fertile window?
Roughly the 5 days before ovulation, the day of ovulation and the day after, because sperm can survive for several days.
Is this tracker accurate?
It’s an estimate based on your past cycles. Stress, illness, travel and hormonal changes can all shift a period.
Can I use it as contraception?
No. Calendar predictions aren’t reliable enough to prevent pregnancy.
Sources
Last updated: