Pregnancy calculator by week
Your starting date
An estimate by calculation, not medical advice: only the dating scan and follow-up by a midwife or doctor set the due date. Nothing is sent; the date stays on your device if you ask.
Gestational age in weeks, weeks since conception, trimester and due date, computed from the first day of the last period. Free estimate, no account.
Enter the first day of your last period, the conception date or the due date: the page gives the weeks of gestational age and of pregnancy, the trimester and the due date, plus the term used in France. The calculation runs on your device.
| Period | Weeks of gestational age |
|---|---|
| 1st trimester | up to 13 weeks + 6 days |
| 2nd trimester | from 14 weeks to 27 weeks + 6 days |
| 3rd trimester | from 28 weeks |
| Due date (Naegele’s rule) | 40 weeks, or 280 days |
| Term used in France | 41 weeks, or 287 days |
An estimate by calculation, not medical advice: only the dating scan and follow-up by a midwife or doctor set the due date. Nothing is sent; the date stays on your device if you ask.
Frequently asked questions
What is the difference between gestational age and weeks since conception?
Gestational age is counted from the first day of the last period; weeks since conception start about two weeks later. 20 weeks of gestational age are about 18 weeks since conception.
How is the due date calculated?
With Naegele’s rule: 280 days, or 40 weeks, after the first day of the last period. In France the term is set at 41 weeks; the page gives both dates.
How are trimesters counted?
The first runs to 13 weeks and 6 days, the second from 14 weeks to 27 weeks and 6 days, the third from 28 weeks. These limits vary slightly between countries and sources.
Does this replace medical follow-up?
No. It is an estimate from a date; the dating scan and follow-up by a midwife or doctor remain the reference.