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SnapCalculations

Pregnancy Due Date Calculator

Pick how you want to calculate (last period, conception or IVF transfer) and the date to get your estimated due date, trimester dates and how far along you are.

days

28 days is typical. Use 20 to 45.

Pick a date and a cycle length between 20 and 45 days.

How it works

  • From the first day of your last period: due date = that date + 280 days (Naegele's rule), adjusted for cycles longer or shorter than 28 days.
  • From conception: + 266 days. From IVF transfer: + 263 days for a day-3 embryo, + 261 days for a day-5 embryo.
  • Pregnancy weeks are counted from the first day of the last period, so you are about 2 weeks pregnant at conception.
  • The first trimester runs to 13 weeks 6 days, the second to 27 weeks 6 days, and the third until birth.

Worked examples

From the last period

If the last period started on 1 January 2026 (28-day cycle), when is the baby due?

  1. Add 280 days (40 weeks) to the first day of the last period.
  2. 1 Jan 2026 + 280 days.

Answer: 8 October 2026

Try this example

A longer 32-day cycle

When is the due date if the last period began on 1 February 2026 and cycles last 32 days?

  1. A 32-day cycle means ovulation is about 4 days later than in a 28-day cycle.
  2. Add 280 + (32 − 28) = 284 days to 1 Feb 2026.

Answer: 12 November 2026

Try this example

Frequently asked questions

How accurate is a due date?

It is an estimate. Most babies are born within about two weeks either side of it. A dating ultrasound in early pregnancy usually gives the most accurate date.

Does this replace medical advice?

No. Your midwife or doctor will confirm your due date, usually with an ultrasound scan.

Results are estimates for general information and are not financial, medical or professional advice.