Period Calculator

Predict your next three period start dates from your last period and average cycle length.

Predict your next period

Enter the first day of your last period, cycle length and period length.

Result

Next period expected

Expected to end

Following period

Third period

Next period = LMP + cycle length

Each following period adds another full cycle length to the previous predicted start date.

Example: Last period started 1 June 2026, 28-day cycle → next period ≈ 29 June 2026.

Enter the first day of your last period.
Optionally enter your average cycle length and period length — otherwise 28 and 5 days are assumed.
Press Calculate to see your next three predicted period dates.

This tool provides general informational estimates only and is not a substitute for medical advice.

FAQ

How are future period dates predicted?

By adding your average cycle length to the first day of your last period, repeated for each upcoming cycle.

What if my cycle is irregular?

Predictions are less accurate with irregular cycles since they assume a consistent cycle length. Track a few cycles for a more reliable average.

What is a typical cycle length?

Cycles typically range from 21 to 35 days, with 28 days being the commonly used average.

Does period length affect the prediction?

No, it doesn't change the start dates — it's shown only as a reference for how long each period is expected to last.