Due Date Calculator

Work out your estimated due date from your last period, conception date or IVF transfer.

Calculate Your Due Date

Enter your last menstrual period or conception date

First day of last period

Conception date

IVF: day-3 embryo transfer

IVF: day-5 (blastocyst) transfer

First day of last period

Usual cycle length (days)

Quick answer

Your estimated due date is 280 days (40 weeks) after the first day of your last menstrual period — Naegele's rule — or 266 days after conception. Only about 1 in 20 babies arrives on the due date itself; most are born between 37 and 42 weeks.

How the due date is calculated

Pregnancy is counted from the first day of your last menstrual period (LMP), about two weeks before you actually conceive. Adding 280 days to the LMP gives the estimated due date. A quick way to do it by hand is to add one year, subtract three months and add seven days.

That rule assumes a 28-day cycle. If your cycles are longer or shorter, ovulation shifts too, so the due date moves by the same number of days (for example, a 32-day cycle adds four days).

If you know the conception date, add 266 days. After IVF, count 266 days from egg retrieval, which is 263 days after a day-3 embryo transfer or 261 days after a day-5 (blastocyst) transfer.

An early ultrasound is the most accurate way to date a pregnancy. If a first-trimester scan (measuring crown–rump length) differs from your period-based date by more than about a week, your doctor will usually change your due date to match the scan.

Trimester dates

Weeks are counted from the first day of your last period.

Stage	Weeks	What happens
First trimester	1–13	Organs form; first scan and screening tests
Second trimester	14–27	Anatomy scan at 18–22 weeks; you feel movements
Third trimester	28–40	Rapid growth; regular check-ups and birth planning
Early term	37–38	Baby is ready, but a little more time helps
Full term	39–40	The healthiest time for most babies to be born
Late / post term	41–42+	Your team will discuss monitoring or induction

Frequently asked questions

How accurate is a due date?

It is an estimate. Only about 4–5% of babies are born on their due date; around 9 in 10 arrive within two weeks either side of it.

My cycles are irregular — can I still use this?

Yes, but the result is less reliable. An early ultrasound gives the most accurate due date when cycles are irregular or you are unsure of your last period.

How do I calculate an IVF due date?

Add 263 days to a day-3 embryo transfer date or 261 days to a day-5 blastocyst transfer date. Your fertility clinic will confirm it.

Can my due date change?

Yes. If your first-trimester scan measures your baby as more than about a week older or younger than your period-based date, your due date is usually updated to the scan date.

How many weeks pregnant am I?

Count the full weeks since the first day of your last period. The calculator shows this along with your current trimester.

Call your doctor or maternity unit straight away if you have

Vaginal bleeding or fluid leaking
Severe or constant tummy pain
Fewer baby movements than usual (from about 24–28 weeks)
A severe headache, vision changes or sudden swelling of the face or hands
A fever, or pain or burning when you pass urine

In an emergency call 112 (India) or 911 (US). This tool gives general information, not medical advice.

Sources

Try next

Expecting? Listen to 280 daily Garbh Sanskar pregnancy stories in Hindi, English and Hinglish on Garbh Katha.

See all free parenting tools →