✿Free calculator

Pregnancy due date calculator

Find your estimated due date from the first day of your last period, the date of conception or an IVF transfer – plus your current pregnancy week.

Calculate from
Average cycle length
Estimated due date
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1st trimester2nd trimester3rd trimester
Today you are
Trimester
Days to go
Likely conception

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How to use the due date calculator

  1. Choose how to calculate: from your last period, from the conception date or from an IVF transfer.
  2. Enter the date. For the last-period method you can set your usual cycle length.
  3. You will see the estimated due date, how many weeks and days pregnant you are today, your trimester and how many days are left.

How the due date is calculated

Doctors count a pregnancy from the first day of the last menstrual period (LMP), not from conception. A typical pregnancy lasts 280 days (40 weeks) from the LMP. This is known as Naegele’s rule:

Due date = first day of last period + 280 days

If your cycle is longer or shorter than 28 days, ovulation happens later or earlier, so the date is moved by the difference. From a known conception date the due date is 266 days later; after a day-5 embryo transfer it is 261 days later, after a day-3 transfer 263 days.

Worked example

If your last period started on 1 January 2026 and you have a 28-day cycle, your estimated due date is 8 October 2026. With a 32-day cycle it moves four days later, to 12 October 2026. A day-5 embryo transfer on 20 January 2026 gives the same due date of 8 October.

Trimesters

TrimesterWeeks
FirstWeeks 1 to 13
SecondWeeks 14 to 27
ThirdWeek 28 until birth

How accurate is a due date?

Only a small share of babies – roughly 4 to 5% – arrive exactly on their due date. Most are born within two weeks either side of it, and a birth between 37 and 42 weeks is considered normal. An early ultrasound scan can date a pregnancy more accurately than the last-period method, so your midwife or doctor may adjust your due date after your first scan.

This calculator gives an estimate for information only and is not medical advice. Always follow the dates and advice from your midwife or doctor.

Frequently asked questions

How many weeks pregnant am I?
Count the weeks from the first day of your last period. The calculator shows this as weeks and days, for example “10 weeks 3 days”, which means you are in your 11th week.
Can my due date change?
Yes. If an ultrasound scan measures the baby as older or younger than expected, especially in the first trimester, your due date may be updated.
Why is pregnancy 40 weeks if conception happens around week 2?
Because pregnancy is counted from the last period, about two weeks before conception. The baby itself develops for about 38 weeks.

Last reviewed: November 13, 2026

Results are estimates for general information only and are not financial, tax, medical or legal advice. Check important figures with a qualified professional.