Due Date Calculator

How to estimate your due date

1. Choose a method: last period, conception date, or ultrasound.
2. Enter the date it asks for.
3. For the last-period method, set your average cycle length.
4. Read your estimated due date, how far along you are, and the trimester.

How the due date is worked out

The common way to calculate due date figures, working out the due date from last period, is Naegele's rule: add 280 days, which is 40 weeks, to the first day of your last menstrual period. As an EDD calculator it gives the estimated date of delivery. This assumes a regular 28-day cycle with ovulation around day 14, so a longer or shorter cycle shifts the date, and this due date calculator adjusts for the cycle length you enter. From a known conception date it instead counts about 266 days. From an ultrasound it uses the gestational age the scan measured.

Why a scan overrides the dates

Dating from a last period is only as good as the cycle behind it, and many cycles are not exactly 28 days or are hard to date. An early ultrasound measures the baby directly and is more accurate, so when a scan date differs from the last-period estimate, the scan is the one your care team uses. Treat the last-period result as a first estimate that a scan can revise.

How accurate is a due date

A due date is a target, not a deadline. Only about 1 in 20 babies are born on the exact due date, and a normal, full-term birth can happen anywhere from three weeks before to two weeks after it. So the estimated due date is a midpoint to plan around, not a fixed day.

Sources: Naegele's rule as described by the American College of Obstetricians and Gynecologists (ACOG) and the UK National Health Service (NHS).

An estimate, not medical advice

Every figure here is an estimate that varies by cycle and by person. It cannot account for your individual pregnancy, and it is not a diagnosis or medical advice. Your doctor or midwife confirms your dates and due date, usually with an ultrasound. Always follow their guidance.

FAQ

How do I calculate my due date?

The usual method adds 280 days to the first day of your last period, which is Naegele's rule. Enter that date and your cycle length and this tool does it, or switch to a conception date or an ultrasound if you have one.

When is my baby due if I know my last period?

Add 40 weeks to the first day of your last menstrual period, adjusted for your cycle length. The tool shows the estimated due date and how far along you are today.

Is a due date from my last period accurate?

It is a reasonable estimate for a regular cycle, but an early ultrasound is more accurate and your care team will use the scan date if the two differ.

Can the due date change?

Yes. An ultrasound often revises it, especially if your cycle is irregular or the dates are uncertain. The due date your doctor or midwife gives you is the one to follow.

Is my information private?

Yes. Everything is calculated in your browser and nothing you enter is uploaded or saved.