Due Date Calculator

The due date calculator estimates your baby’s due date from the first day of your last period or the conception date. It also shows your current pregnancy week, trimester and key dates: conception, first ultrasound, the start of the second and third trimesters and the second screening. The calculation is instant, on your device.

How to use the calculator

Choose a method. “By last period” — enter the first day of your last period: this is the standard method, the due date is 280 days (40 weeks) from that day. “By conception date” — enter the conception date if it is known exactly, for example with IVF: the due date is 266 days (38 weeks). The calculator instantly shows the due date, current week and trimester, plus a table of key dates with marks for what has already passed.

How the due date is calculated

The medical pregnancy count starts from the first day of your last period, not conception — the day of ovulation and conception is hard to pin down, while the first day of a period is easy to remember. Full term is 280 days (40 weeks). If the conception date is known, count 266 days (38 weeks) from it — the result is the same. Conception falls on week 2 of this count.

How accurate is the calculation

This is an estimate: only about 5% of babies are born exactly on the due date, most arrive within a week before or after. With an irregular cycle the date shifts. Your obstetrician refines the date using a first-trimester ultrasound — it is the most informative way to date a pregnancy.

This information is for reference only and is not a medical service or diagnosis.

Frequently asked questions

How do I calculate my due date from my last period?
Add 280 days (40 weeks) to the first day of your last period. Example: period started October 5 — due date around July 12. Enter the date in the calculator and it computes automatically.
Why is pregnancy counted from the period and not conception?
A woman knows the first day of her period exactly, while conception can happen on any of several days around ovulation. So the medical count starts from the period, and conception falls on week 2 of that count.
How do I know my current week of pregnancy?
Count full weeks from the first day of your last period to today and add one — that is your current week. The calculator shows it automatically together with the trimester.
How many weeks does pregnancy last?
Full term is 40 weeks (280 days) from the first day of the last period, or 38 weeks (266 days) from conception. First trimester: weeks 1–13, second: 14–27, third: 28–40.
What if my calculated due date doesn’t match the ultrasound?
Rely on the first-trimester ultrasound date — it is the most accurate dating method. A difference of a few days is usually not significant, but your doctor makes the final call.
Do babies usually arrive exactly on the due date?
No: only about 5% of babies are born on the exact date. Most births happen between weeks 38 and 42, usually within a week before or after the calculated due date.

Updated: Oct 19, 2026

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