Pregnancy Due Date Calculator

The only input is the first day of your last menstrual period (LMP). The tool adds 280 days to it, the convention obstetricians use for the estimated due date, and also shows how many weeks have passed since that date.

For an LMP of 1 October 2026, the estimated due date is 8 July 2027. Checked on 19 October 2026, the current gestational age shows as 2 weeks. This is an estimate from a date you remember, not a diagnosis or a confirmed dating. Your doctor or midwife will confirm the date that goes in your records.

The counter shows completed weeks only, with the days dropped. A period that started on 15 February 2026 is 246 days before 19 October 2026, which is 35 weeks and 1 day, so the tool shows 35 weeks. It counts from the LMP, not from conception, which is the standard way pregnancy weeks are numbered.

The counter goes blank in two cases: if the date you entered is in the future, and if it is more than 45 weeks ago. It keeps counting past the due date, so an LMP of 31 December 2025 gives a due date of 7 October 2026 and shows 41 weeks on 19 October.

ACOG describes first-trimester ultrasound as the most accurate way to establish or confirm gestational age. If your scan date and this tool disagree, the scan date set by your care team is the one to go by.

To make the weeks counter follow the scan, work backwards: subtract 280 days from the scan's due date and enter that as the LMP. A scan due date of 15 July 2027 becomes an entered date of 8 October 2026. The tool will then show the scan's due date and the matching week count.

Few babies arrive on the estimated date itself. One study put the figure at about 4%, and other sources say 4 to 5%. In practice, the due date is better treated as the middle of a stretch of weeks than as an appointment. For dates you need to fix in advance, such as leave from work, ask your midwife or doctor what window they expect for you.