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Due Date Calculator

Enter the first day of your last period and your cycle length to estimate your due date. Estimate only, not medical advice.

The first day of your last period.

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

Source: ACOG Committee Opinion No. 700 (2017) ↗

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

How it is calculated

The calculator uses Naegele’s rule, adjusted for cycle length:

  • Due date = first day of last period + 280 + (cycle length − 28) days
  • Approximate conception = first day of last period + (cycle length − 14) days

Estimate only, not medical advice.

Worked example

First day of last period 10 January 2026:

  1. 28-day cycle: due date 17 October 2026, conception about 24 January 2026
  2. 32-day cycle: due date 280 + 4 days = 21 October 2026

Why your number may differ

Only about 1 in 20 babies arrive exactly on the due date, and an ultrasound dating scan is more accurate. Estimate only, not medical advice.

Frequently asked questions

Will my baby arrive on this date?

Only about 1 in 20 babies arrive exactly on the due date. Treat it as an estimate.

Is there a more accurate way?

An ultrasound dating scan is more accurate. Estimate only, not medical advice.

How does cycle length change the date?

The due date moves later or earlier by the difference between your cycle length and 28 days.

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