Period Calculator (Next Period Dates)
Predict your next six periods from the start of your last period, cycle length and period length.
For general information only — not medical advice. Results are estimates; talk to a doctor or qualified health professional about your own health.
How to use
- 1Enter the first day of your last period.
- 2Enter your usual cycle length and how many days your period lasts.
How it's calculated
Next period start = last start + cycle length; end = start + period length − 1. Repeated for six cycles.
Frequently asked questions
What's a normal cycle length?
Adult cycles typically range from 21 to 35 days (ACOG). It's normal for length to vary by a few days.
When should I see a doctor?
If periods are very irregular, heavy, painful enough to disrupt life, or stop for 3 months or more without pregnancy.
Is my data saved?
No. Everything is calculated in your browser; nothing is stored or sent.