Pregnancy Due Date Calculator

Select the first day of your last menstrual period (LMP).

Last Menstrual Period

Your Estimated Dates

Estimated Due Date

Current Gestational Age
Approximate Conception Date

About Pregnancy Due Date Calculator

Last updated: 25 August 2026

Enter the first day of your last menstrual period and this calculator estimates your due date, your current gestational age in weeks, and which trimester you are in.

How the due date is estimated

It uses Naegele's rule: 280 days — 40 weeks — from the first day of the last menstrual period. The approximate conception date is estimated at LMP plus 14 days, assuming ovulation around the middle of a 28-day cycle. Note the consequence: gestational age is counted from the LMP, not from conception, so you are already counted as two weeks pregnant at the moment of conception.

Worked example: an LMP of 1 January gives an estimated due date of 8 October — 280 days later — with conception around 15 January and the second trimester beginning near 2 April.

How likely is the baby to arrive on the due date?

Only about 4% of births happen on the estimated date itself, and roughly 90% fall within two weeks either side. The due date is the midpoint of a range, not an appointment. If your cycle is longer or shorter than 28 days, or irregular, Naegele's rule is less reliable — an early ultrasound dates a pregnancy more accurately than any calculation from LMP.

Medical note

This is an estimate for general information, not medical advice, and it does not replace antenatal care. Your midwife or doctor will date the pregnancy using ultrasound and clinical assessment, and that date supersedes this one. Seek prompt medical attention for bleeding, severe pain, reduced fetal movement or any concern about the pregnancy — do not use a calculator to decide whether a symptom needs attention.

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