Pregnancy Calculator
Local only — nothing is uploaded unless you save or share it.
Work out your due date, how many weeks you are, and what comes next.
- Enter the first day of your last period — the day bleeding started, not when it ended.
- If your cycle is not 28 days, change the cycle length; the due date moves with it.
- Read the due date, how many weeks you are today, and the milestone dates underneath.
Estimated due date
What comes next
An estimate, not a diagnosis. A dating scan is more accurate, and your midwife or doctor is the one to ask.
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About this tool
Enter the first day of your last period and this works out your estimated due date, how far along you are today in weeks and days, which trimester that puts you in, and the dates of the milestones ahead. It uses Naegele's rule, which is the same arithmetic as the cardboard wheel on a midwife's desk: the due date is 280 days — forty weeks — after the first day of your last period. That rule assumes a 28-day cycle, so there is a box for your own cycle length, and a longer cycle moves everything later by exactly the difference. What it cannot do is be certain. A due date is an estimate, and about one baby in twenty-five actually arrives on it; most come within a fortnight either side. If you have had a dating scan, that measurement is more accurate than any calculation from a date, and it is the one to go by. This is arithmetic you can check, not a medical opinion, and it is no substitute for your midwife or doctor. Nothing you type is sent anywhere. The dates stay in your browser, which for this of all calculations seemed like the right default rather than a feature to advertise.
Frequently asked questions
How is the due date calculated?
By Naegele's rule: 280 days, or forty weeks, from the first day of your last period. It is the standard method and the same one a midwife's wheel uses. Because it counts from your last period rather than from conception, you are counted as two weeks pregnant at the moment you conceive, which surprises almost everybody the first time.
How accurate is a due date?
Not very, and that is normal. Roughly four per cent of babies are born on their estimated date; most arrive within two weeks either side of it. A dating scan in the first trimester is more accurate than any date-based calculation, so if you have had one, use the date it gave you.
What if my cycle is not 28 days?
Change the cycle length and the due date moves by the difference. Naegele's rule assumes ovulation on day 14 of a 28-day cycle, so a 35-day cycle ovulates about a week later and the due date is about a week later too. If your cycles are very irregular, a scan will date the pregnancy far better than any cycle-based estimate.
Why does it say I was already two weeks pregnant at conception?
Because pregnancy is counted from the first day of your last period, not from conception — that is the convention every hospital and every scan uses. Conception happens around two weeks into that count, so gestational age is always about two weeks ahead of the age of the embryo.
Is anything I enter stored or sent anywhere?
No. The calculation runs in your browser and the dates never leave your device. Nothing is uploaded, nothing is logged against you, and there is no account involved.
Can this tell me anything about the health of the pregnancy?
No. It is date arithmetic and nothing more. It cannot tell you whether a pregnancy is progressing normally, and it is not a substitute for antenatal care. Anything that worries you is a question for a midwife or doctor, not a web page.
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