🩸 Period Calculator
Predict your next few period start dates and your most fertile window based on your average cycle.
Your Cycle Details
Your Prediction
| Cycle | Predicted Start Date | Expected End |
|---|
Predictions are estimates based on averages and can vary due to stress, health, and lifestyle factors. This is not a form of contraception.
How the Period Calculator Works
This calculator uses the first day of your last period, plus your average cycle length, to project when your next several periods are likely to start. It also estimates your fertile window, the days around ovulation when pregnancy is most likely.
Formula
Ovulation (est.) = Next period start − 14 days
Fertile window = Ovulation day − 5 days to Ovulation day + 1 day
Limitations
Cycle length can vary month to month, so these dates are estimates rather than guarantees. Tracking your cycles over several months improves accuracy.
Frequently Asked Questions
How accurate is a period predictor?
It is most accurate for people with regular cycles. Irregular cycles make predictions less reliable, so tracking over time is recommended.
What is the fertile window?
The fertile window is the approximately six-day span ending on the estimated ovulation day, when conception is most likely to occur.
Can I use this as birth control?
No. This calculator provides estimates only and should not be relied on as a method of contraception.