Due date calculator

How is the due date worked out?

Pregnancy is counted from the first day of the last period: the due date is 40 weeks (280 days) later, and a pregnancy normally lasts 37 to 42 weeks. Conception, IVF transfer and ultrasound dates are adjusted to that same scale, so the weeks you see here match the weeks your doctor or midwife uses.

Source: NHS: Due date calculator

How reliable is it?

It is an estimate. Only about 4 to 5 percent of babies are born on their due date, and most arrive within a couple of weeks either side. Think of it as the middle of a window, not a deadline.

What if her cycles aren't 28 days?

With the last period method, set the cycle length: a longer cycle means later ovulation, so the date moves later, and a shorter one moves it earlier. If her cycles are irregular or the date is uncertain, an early ultrasound can confirm or correct the due date.

Source: NHS: Due date calculator

What do I do with the date?

Tell your OB or midwife. They confirm it, often with an ultrasound, and plan scans and checkups around it. Then add it in The Dad Center app, and your weekly briefing and task list follow the right week.