Period Calculator — When Will My Period Come?
Predict your next 6 period dates instantly. Enter your last period start date and average cycle length — no sign-up required.
Calculate Your Next Periods
Your next 6 predicted periods
How the period calculator works
The calculator adds your cycle length repeatedly to your last period's start date to project future periods. If your last period started on 1 June and your cycle is 28 days, the next period is predicted for 29 June, then 27 July, and so on.
How accurate are period predictions?
Predictions are based on your average cycle length. Real cycles vary by a few days due to stress, travel, illness, weight changes, or hormonal fluctuations. According to a large-scale study of over 600,000 menstrual cycles (Symul et al., 2019), the median cycle-to-cycle variation is approximately 3–4 days. Expect predictions to be within ±3–5 days for most people.
For a full interactive calendar with ovulation, fertile window, and history management, use our full Period Tracker.
What counts as a "late" period?
A period is generally considered late if it hasn't arrived 7 or more days after its predicted date. If you are sexually active and your period is more than 7 days late, take a pregnancy test. If it's more than 2–3 weeks late and pregnancy is ruled out, consult a healthcare provider. See our guide on reasons for late periods.
Period Calculator FAQ
How do I calculate when my period will come?
Add your average cycle length to the start date of your last period. If your last period started 1 June with a 28-day cycle, your next period is predicted for 29 June.
Why is my period calculator date different from my actual period?
Cycle predictions are based on your average cycle length. Real cycles vary by a few days due to stress, illness, weight changes, or hormonal shifts. A ±3-day variation is completely normal.
Can I use the period calculator for irregular periods?
Yes, as a rough guide using your average cycle length. For more personalised tracking, use our full Period Tracker, which calculates your actual average from your logged history.