Due date calculator
You calculate a due date by adding 280 days to the first day of your last period — the convention midwives use — and correcting that for your own cycle length. Below you can also count from conception, an IVF transfer or a digital test. You get a term window back rather than one date, because almost nobody gives birth on the estimated day itself.
Calculate your due date
Your longest cycle cannot be shorter than your shortest one. Swap the two numbers and we will carry on.
This calculation works with cycles of 21 to 45 days. If that was a typo, correct the number. If it is right — with PCOS, for instance, a long or highly variable cycle is perfectly common — then your pregnancy cannot be dated reliably from the calendar. An early dating scan in the first trimester gives the most accurate date.
A digital pregnancy test with a weeks indicator counts the weeks since conception, not since your last period. The manufacturer states the indicator is 93% accurate at detecting when you conceived, and beyond roughly six weeks after conception your hCG is too high for the estimate to hold.
Your due date
You are now weeks pregnant
A pregnancy counts as term from 37 weeks up to 42 weeks. 42 0/7 weeks is the first day AFTER that window, not the last day inside it.
A due date is not a deadline. Around 4% of women give birth on that exact day; everyone else gives birth around it, usually inside the window above.
Your test counts the weeks since conception. Your midwife counts from your last period, roughly 2 weeks earlier — which is why the number of weeks above is higher than the one on your test.
Because your cycle varies, a date taken from the calendar is less reliable for you. An early dating scan in the first trimester dates a pregnancy more accurately; discuss that with your midwife or GP.
View the pregnancy blood testThis calculation is an estimate based on the dates you enter, not a measurement. A scan in the first trimester dates a pregnancy more accurately and always takes precedence. Discuss your due date with your midwife, GP or gynaecologist.
Calculating your due date after IVF
After IVF the transfer date is known, so nothing has to be inferred from your cycle. For a blastocyst (day 5) you add 261 days to the transfer date, and for a day 3 embryo 263 days; both come to 266 days from conception. An IUI is counted from the insemination itself, because it is timed to ovulation. Choose "IVF or IUI" above and pick the treatment you had.
Calculating your due date from conception
If you know the day of conception — from an ovulation test or a temperature chart, say — the calculation adds 266 days to it. That is the same convention as the 280 days from your period, fourteen days further into the cycle. Mind the wording that follows from it: your midwife will call you "six weeks pregnant" when conception was four weeks ago.
Your due date on an irregular cycle
When a cycle varies it is mostly the first half that moves, and with it the timing of ovulation. Enter your shortest and your longest cycle and the tool works out both, giving you a period instead of one date. That period hides nothing: it shows how much room your own input genuinely leaves. An early dating scan in the first trimester remains the most accurate way to date a pregnancy.
How many weeks pregnant are you?
Gestational age is counted from the first day of your last period, so you are already about two weeks "pregnant" at conception. The tool shows those weeks and days as soon as you enter a date, in the form you will hear in the consulting room: 8 + 3 means eight weeks and three days.
Frequently asked questions
How do you work out a due date?
You add 280 days to the first day of your last period and correct for your cycle length: if your cycle runs 32 days instead of 28, the date moves four days later. Those 280 days are a convention rather than a measured average — they are kept because your midwife works with the same number. If you know the date of conception or of an IVF transfer, counting from there is more precise.
How many weeks pregnant are you if Clearblue shows 1-2?
Roughly 3 to 4 weeks. A Clearblue digital test shows the weeks since conception, while your midwife counts from your last period, about two weeks earlier. So "1-2 weeks" on the display means 3-4 weeks pregnant, "2-3 weeks" means 4-5 weeks and "3+ weeks" means 5 weeks or more. The manufacturer states that indicator is 93% accurate at detecting when you conceived, and beyond roughly six weeks after conception your hCG is too high for the estimate to hold.
How do you work out when you conceived?
Conception happens around ovulation, and ovulation falls roughly fourteen days BEFORE your next period — not fourteen days after your last one. Counting back from your due date puts it about 266 days earlier. After an IUI or IVF you know it exactly: the insemination or the transfer is the starting point.
How do I calculate a date?
Choose above what you want to count from — your last period, conception, an IVF transfer or a digital test — and enter that one date. The calculation runs in your browser; nothing is stored or sent anywhere. You get your due date with the term window around it, plus how many weeks pregnant you are now.
Further reading
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This calculation is an estimate based on the dates you enter, not a measurement. A scan in the first trimester dates a pregnancy more accurately and always takes precedence. Discuss your due date with your midwife, GP or gynaecologist.