Pregnancy Calculator

A pregnancy is counted in weeks from the first day of the last period, so the due date is 280 days (40 weeks) after it. That is Naegele's rule. A cycle longer or shorter than 28 days usually means ovulation came later or sooner, so the due date moves by the difference: a 35-day cycle adds 7 days.

From a conception date, the due date is 266 days later, and the weeks are counted from 14 days before it. From an IVF transfer, it is 261 days after a day 5 transfer and 263 days after a day 3 one. From a known due date, everything else is counted back from it.

The first trimester runs to 13 weeks 6 days, the second from 14 weeks to 27 weeks 6 days, and the third from 28 weeks. The anatomy scan is usually offered between 18 and 22 weeks, and 37 weeks counts as full term. Dates are whole calendar days on this device, so time zones and clock changes never move them.

Most babies arrive within two weeks either side of the due date. A dating scan early in pregnancy is more accurate than any date sum, so go by the date a midwife or doctor gives. This is not medical advice.

What you enter is saved on this device so you can come back to it. Clear all empties it, and Undo brings it back.