Pregnancy due date calculator
Health & fitnessHow far along is your pregnancy?
Estimate your due date, pregnancy week and trimester from a period, conception or IVF transfer date.
What you enter stays on your device while you use this tool. Opening a shared link sends the settings in its address to HowToolbox to prepare the page.
20–45 days; irregular cycles make this estimate less reliable.
Leave empty for today.
Nothing is stored by this tool. If you choose to include personal details in a copied link, it contains the dates. Share it carefully.
Estimated due date
Enter a date
Estimate only. Ask your midwife or doctor to confirm your dates; a dating scan may change the estimate.
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Estimate your due date, pregnancy week and trimester from a period, conception or IVF transfer date.
How to use
- Choose your dating method and enter the relevant date.
- For the last-period method, adjust your usual cycle length if it is not 28 days. Leave the week-on date empty to use today.
- Read the estimate and milestones. Confirm the dates with your midwife or doctor.
How it works
The last-period method uses Naegele’s rule: due date = the first day of the last period + 280 days + (cycle length − 28 days). For a 28-day cycle starting on 1 January 2026, this gives 8 October 2026. The cycle adjustment assumes ovulation about 14 days before the next period.
From a known conception date, add 266 days. ACOG’s Methods for Estimating the Due Date gives 263 days after a day-3 embryo transfer or 261 days after a day-5 transfer. The conception date is not necessarily the day of sex.
Pregnancy weeks count from the estimated due date minus 280 days, including about two weeks before conception. ACOG defines the second trimester as starting at 14 weeks and the third at 28 weeks. The table gives calendar estimates, not appointments or a prediction of when birth will occur.
The NHS due date calculator notes that a dating scan may provide a more accurate estimate. Irregular cycles, uncertain dates and variation between pregnancies limit this calculation. It cannot confirm a pregnancy or its progress; ask your midwife or doctor.
Worked example
What due date follows a day-five embryo transfer on Feb 1, 2026?
- For a day-five transfer, add 261 days to the transfer date.
The estimated due date is Oct 20, 2026.
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Frequently asked questions
Why do pregnancy weeks start before conception?
Gestational age conventionally starts from the last period, roughly two weeks before conception in a 28-day cycle. IVF dates are converted to the same scale.
Are my dates saved?
Nothing is stored by this tool. Personal details are excluded from links by default. If you explicitly include them, the copied link contains the dates.
Why is there no pregnancy week for my selected date?
The date may be before the estimated gestational start or beyond 42 weeks. The due date remains available for reference; the calculator does not assume an ongoing pregnancy beyond that range.
How accurate is the due date?
It is an estimate: only about 4% of babies are born on the day, and most arrive within two weeks either side of it. A dating scan early in pregnancy gives a more precise date.
Why do some countries give the due date at 41 weeks?
France dates the expected birth at 41 weeks of amenorrhoea (SA), counted from the last period; most countries use 40 weeks (280 days). The calculator uses 40 weeks, so a French due date falls a week later.
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