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Period Calculator

Enter the first day of your last period, your cycle length and period length to see your next three period dates. Estimate only, not medical advice.

Days from the first day of one period to the first day of the next (20 to 45). Usually 28.

How many days your period usually lasts (1 to 10).

This result is an estimate only. Check with your bank or the relevant authority before making decisions.

How it is calculated

  • First period = first day of last period + cycle length
  • Second period = first day of last period + 2 × cycle length
  • Third period = first day of last period + 3 × cycle length
  • First period ends = first period date + period length − 1

Estimate only, not medical advice.

Worked example

First day of last period 10 January 2026, 28-day cycle, 5-day period:

  1. Next period: 7 February 2026
  2. Second period: 7 March 2026
  3. Third period: 4 April 2026
  4. Next period ends: 11 February 2026

Why your number may differ

Cycles of 21 to 35 days are commonly considered typical for adults, so real dates can differ from the prediction. See a doctor if your periods change a lot. Estimate only, not medical advice.

Frequently asked questions

What is a typical cycle length?

Cycles of 21 to 35 days are commonly considered typical for adults.

When should I see a doctor?

See a doctor if your periods change a lot. Estimate only, not medical advice.

How are the dates calculated?

Each period is your cycle length added to the first day of your last period, repeated.

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