🩸 Period Calculator
A regular cycle is beautifully predictable: add your average cycle length to the first day of your last period, repeat, and you have your calendar for the next few months.
This calculator projects your next three period start dates. Stress, travel, illness and hormonal changes can shift real dates, so treat the farthest predictions as approximate.
How to use this calculator
Enter the first day of your last period and your cycle length to predict your next three periods.
- Pick the First day of last period on the date field.
- Enter your Average cycle length in days.
- Read the headline next period date.
- Check the two following dates to plan further ahead.
Frequently asked questions
How are the dates predicted?
Each date is your last period start plus one, two and three cycle lengths. With a last period of 1 September 2026 and a 28-day cycle, the next three start on 29 September, 27 October and 24 November 2026.
What if my cycle is not exactly regular?
Small wobbles are normal and the near date stays useful, but the farther predictions drift. If your cycle varies a lot, track a few months to find your real average.
Can stress delay my period?
Yes. Stress, travel, illness, heavy training and weight changes can all push ovulation later and with it the period. The calculator assumes a steady rhythm.
When should I see a doctor?
If periods stop for three months, cycles are consistently shorter than 21 or longer than 35 days, or bleeding is very heavy or painful, get checked rather than relying on predictions.