Due Date Calculator

How this estimate is worked out

The calculator counts forward from the first day of your last menstrual period. The American College of Obstetricians and Gynecologists (ACOG) describes the convention in its Committee Opinion on methods for estimating the due date: “By convention, the EDD is 280 days after the first day of the LMP.” EDD means estimated due date and LMP means last menstrual period.

That count starts at the first day of your period, not at conception. The same ACOG text says the practice assumes a regular menstrual cycle of 28 days, with ovulation on the 14th day, and that it does not account for inaccurate recall of the last period, irregular cycles or variability in when ovulation happens.

If your cycle is not 28 days

You can enter your usual cycle length, counted from the first day of one period to the first day of the next. The NHS describes cycles ranging from every 21 days to every 35 days, so the calculator accepts a whole number of days from 21 to 35 and uses 28 when you leave it alone.

For another length, the calculator adds or takes away the difference from 28 days: a 35-day cycle adds 7 days to the 280, and a 21-day cycle takes 7 away. That adjustment is simple arithmetic that follows from the 28-day assumption above. It is our own estimate, adjusted for your cycle length, and not a formula published by ACOG or the NHS. If your cycles vary from month to month, or you are not sure of the date, treat the result as a rough estimate and ask your provider.

What an estimated due date is, and is not

An estimated due date is a planning date, not the day your baby will be born. The NHS says: “Pregnancy normally lasts from 37 weeks to 42 weeks from the first day of your last period.” The date you are given sits inside that range, and your provider may move it once your dates are confirmed.

This page shows you one date and the number of days until it, counted on the calendar from today. It does not tell you how your pregnancy is going, whether anything is normal or when to call. For anything about your health, your provider is the person to ask.

Your provider will confirm your dates

An estimate from your last period is a starting point. In England the NHS offers a dating scan, described on its 12-week scan page as an ultrasound at around 10 to 14 weeks of pregnancy that checks your dates and works out your due date. Where you live, your midwife or doctor will tell you how and when your dates are confirmed.

If your provider has already given you a due date, use theirs rather than this estimate. This calculator is for planning around a date, for example to see how far away it is.

What to do with your date

Write the date down with the date your last period began, and bring both to your next appointment. Several free tools on this site ask for a due date: the Birth Plan Builder, the Contraction Timer for when labor starts and the First Weeks Home Planner for once your baby has arrived. Use the date your provider gave you, or this estimate until they do.

Press Print to get a one-page record with the date you entered, your cycle length, the estimated date and the days until it. Nothing is sent anywhere; save a copy on this device or print it before you close the page.