Period Calculator
Enter a valid date and a cycle length between 21-45 days.
| Cycle | Estimated start date |
|---|
These are estimates based on your average cycle length — actual cycles vary in length even for people with regular periods. Track a few real cycles for a more personalized prediction.
Free period calculator that predicts your next 6 cycles from your last period date and average cycle length — not just the next one.
How it works
- Enter the first day of your last period
- Enter your average cycle length
- See your next 6 predicted period start dates
Frequently asked questions
Why predict 6 cycles instead of just the next one?
Seeing several months ahead makes it easier to plan around travel, events, or just to spot the pattern of your cycle at a glance, rather than recalculating one period at a time.
How accurate are these predictions?
They're based on your average cycle length staying consistent — actual cycles vary in length even for people with regular periods, so treat further-out predictions as less certain than the next one or two.
Related tools
From the blog
Update history
- 2026-09-03 Bounded numeric fields are now sliders instead of number inputs.
- 2026-09-01 Added: a cover image — used as the card thumbnail, social share image, and blog title image.
- 2026-09-01 Launched: period calculator predicting the next 6 cycles from last period date and average cycle length. Entirely client-side.