سهلSahel

Pregnancy Calculator

Estimated due date and how far along you are

calendar_today Last updated: August 22, 2026

What the clinic dates from

Gestational age is counted from the last period, not from conception — the convention every clinic and scan report uses. An estimate, not medical advice: a first-trimester dating scan is more accurate than any calculation. Worked out in your browser; nothing is sent anywhere.

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Sahel's pregnancy calculator works out the estimated due date, gestational age in weeks and days, and the current trimester — from the first day of your last period, a conception date or an IVF transfer — adjusts the date for your cycle length, and shows the milestones ahead along with the due date on the Hijri calendar.

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How does this tool work?

1

Pick what you know

Last period, conception date, IVF transfer, or a due date from a scan.

2

Enter the date

With a last period, set your cycle length so the date is adjusted.

3

See the dating

Due date, weeks along, the current trimester, and the milestones ahead.

Frequently asked questions

How is the due date calculated? expand_more
By Naegele's rule: 280 days, or forty weeks, from the first day of your last period. The tool adjusts that for your cycle length — on a 35-day cycle ovulation is a week later and so is the due date, an adjustment many calculators skip, which is why theirs come out early.
Why does it say I am two weeks along before I conceived? expand_more
Because gestational age is counted from the first day of your last period, not from conception, and there are about two weeks between the two. That is the convention the clinic, the scan report and the maternity leave form all use, so the tool follows it and reports the estimated conception date separately.
What is the difference between a day-3 and a day-5 IVF transfer? expand_more
A day-5 blastocyst is already five days past fertilisation at transfer; a day-3 embryo is three. So the due date is 261 days from a day-5 transfer and 263 from a day-3 one — which is why the tool asks which kind of transfer it was, not just the date.
When does each trimester end? expand_more
The first runs from week 0 through the end of week 13, the second from 14 through the end of 27, and the third from 28 until birth. The tool dates each of these, along with the anatomy scan, viability, and the four term stages: early term at 37 weeks, full term at 39, late term at 41, and post-term at 42.
Does this replace a dating scan? expand_more
No. A first-trimester dating scan is more accurate than any calculation, which is why you can enter the due date it gave you and have everything else worked back from it. This is an estimate, not medical advice.

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