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CALCULATOR · Health

Pregnancy Calculator

Estimate your due date, current week and trimester from the first day of your last period.

Show formula
EDD = LMP + 280 days + (cycle − 28) — Naegele/Parikh

Method reviewed:Naegele’s rule with Parikh’s cycle-length adjustment · reviewed August 2026

Inputs

Calendar

Every date field, picker and result uses this calendar.

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Result

Your result appears here

Enter First day of last period and the result fills in as you type.

How it works

  1. Enter the first day of your last period.
  2. Adjust the average cycle length if it differs from 28 days.
  3. Read the estimated due date, current week and trimester.

Frequently asked questions

How accurate is the estimated due date?

It is a population-level estimate: only around 4% of babies arrive on their exact due date. Ultrasound dating by a clinician is more precise.

Why does cycle length shift the due date?

The rule assumes ovulation 14 days before the next period. Longer cycles imply later ovulation, so the estimate moves by (cycle − 28) days.

Is this medical advice?

No. This tool is informational only — always confirm dates with a healthcare professional.

Examples

Last period started on 1 March 2026, 28-day cycle
Due date 6 December 2026 — 280 days (40 weeks) after the first day of that period. Conception most likely happened around 15 March 2026.
The same start date with a 32-day cycle
Due date 10 December 2026. Each day the cycle runs past 28 moves ovulation, and with it the due date, one day later.

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