Due Date Calculator
Estimate a pregnancy due date by adding 280 days to the first day of the last menstrual period.
Quick answer: enter your details below and click Calculate — your result appears instantly, right here in your browser. Nothing you enter is uploaded or stored.
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Calculators
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How to use
- Enter the first day of your last menstrual period.
- Read the estimated due date.
- Note that the date is an estimate, not a guaranteed delivery day.
About this tool
The standard estimate counts 40 weeks, or 280 days, from the first day of the last menstrual period, which is roughly two weeks before conception in a typical cycle. Enter that date and the tool returns the estimated due date. The result is general information only, not medical advice, and only a small share of births land exactly on the estimated date — an ultrasound gives a more reliable estimate.
Frequently asked questions
Why count from the last period instead of conception?
Conception day is often unknown, while the last period is usually remembered, so the 280-day count is the standard convention.
How often are babies born on their due date?
Only a small minority arrive exactly on the date; most arrive within a couple of weeks either side.