Free tool · Pregnancy
Due date calculator.
Work out your baby’s due date and how many weeks pregnant you are, from your last period, your conception date, an IVF transfer or a scan. You’ll also see your trimesters and key dates ahead.
Four methods
Week by week
Fully private
Always free
How it works
How your due date is worked out.
How is a due date calculated?
A due date is usually 280 days (40 weeks) after the first day of your last period. If you know when you conceived, it is 266 days (38 weeks) after conception. Your doctor may adjust it after an early ultrasound scan, which is the most accurate way to date a pregnancy.
01
Last period
We add 280 days to the first day of your last period, and adjust for cycles longer or shorter than 28 days.
02
Conception
If you know the date you conceived, we add 266 days, the average time from conception to birth.
03
IVF transfer
We add 266 days to the transfer date and take away the embryo’s age: 261 days for a day-5 embryo, 263 for day 3.
04
Ultrasound scan
If a scan told you how many weeks and days you were, we count forward from that. Early scans are the most accurate.
Good to know
Your weeks, explained.
Pregnancy is counted from the first day of your last period, about two weeks before you actually conceive. That is why you are already considered “four weeks pregnant” when a test first turns positive.
The three trimesters
- First trimester: from the start up to 13 weeks and 6 days
- Second trimester: 14 weeks to 27 weeks and 6 days
- Third trimester: 28 weeks until your baby is born
Few babies arrive on the day
Your due date is an estimate. Only a small share of babies are born on it, and most arrive in the two weeks either side. From 37 weeks your baby is considered full term. If your doctor gives you a different date after a scan, follow theirs.
Call your doctor or hospital straight away if you have
- Bleeding from the vagina, or fluid leaking
- Severe or constant tummy pain
- A severe headache, blurred vision or sudden swelling of the face, hands or feet
- A fever, or feeling very unwell
- Your baby moving less than usual, or a change in their pattern of movements
Plan your first forty days early
Around 30 weeks is a good time to think about the weeks after birth: who will help, what you will eat and how you will rest. Our postnatal care at home plans run for 7, 14, 28 or 40 days.
Questions
Frequently asked questions.
How accurate is my due date?
It’s an estimate. Most babies are born within two weeks either side of it. A due date from an early ultrasound scan is usually more accurate than one from your last period.
Why does pregnancy count from my last period?
Most women know when their last period started but not the day they conceived, so doctors count from the period. It adds about two weeks before conception to your pregnancy.
How many weeks is full term?
From 37 weeks your baby is considered full term. A typical pregnancy is counted as 40 weeks from the first day of your last period.
My scan gave a different due date. Which is right?
Follow the date your doctor gives you after your scan. Measuring your baby early in pregnancy dates it more accurately than counting from a period.
How is the due date worked out after IVF?
From your embryo transfer date. Add 261 days for a day-5 embryo, or 263 days for a day-3 embryo. Your fertility clinic will confirm your date.
Is my information saved anywhere?
No. The calculator works entirely on your phone or computer. Nothing you type is stored or sent to us.
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