Pregnancy Due Date Calculator

Choose what you know and the calculator works out the rest.

1. Under I know, pick First day of my last period (the usual starting point), Conception date (if you tracked ovulation or had fertility treatment) or My due date (a date from a scan or your midwife).
2. Enter that date in Date.
3. Read the estimated due date and the status line under it, which gives your weeks and days pregnant today and your trimester.
4. Scroll to the milestone table for dates and a countdown to each.

Further rows show the estimated first day of the last period, the estimated conception date, days until the due date and the percentage of the pregnancy completed. If the date you enter is in the future, or more than 42 weeks ago, the status line says so.

The tool uses Naegele's rule. Pregnancy is counted from the first day of the last menstrual period (LMP) and lasts 40 weeks, so due date = LMP + 280 days. Conception is assumed about two weeks after the LMP: conception = LMP + 14 days. If you start from a conception date the tool subtracts 14 days to find the LMP, and if you start from a due date it subtracts 280.

Worked example: an LMP of 1 March 2027 gives conception around 15 March 2027 and a due date of 6 December 2027. Entering 15 March as the conception date, or 6 December as the due date, returns the same set of dates. The milestone table then reads 13 weeks on 31 May 2027, 20 weeks on 19 July, 28 weeks on 13 September, 37 weeks on 15 November, 39 weeks on 29 November and 42 weeks on 20 December.

Your current week is the number of whole weeks since the LMP, with the extra days beside it. The first trimester covers weeks 0 to 13, the second weeks 14 to 27, and the third starts at 28 weeks.

Only about one baby in twenty arrives on the due date. Most arrive within two weeks either side, and 37 to 42 weeks is the usual range. The estimate is weaker when:

• your cycles are much longer or shorter than 28 days, or irregular, because ovulation may not fall on day 14. The tool assumes 28 days and has no cycle length field;
• you are unsure of the LMP date, for instance after stopping hormonal contraception;
• you conceived through IVF. Use the due date your clinic gave you under My due date instead of an LMP.

A dating scan, usually in the first trimester, can change the due date if it measures differently from the period-based one, and the scan date normally takes precedence afterwards. The results are general estimates and not medical advice; your midwife or obstetrician gives the date that applies to your care. The tool does not adjust for twins or other multiples.

Once the baby has arrived, the age calculator tracks their age in weeks and months. To count days between appointments use the date difference calculator, and the countdown timer can count down to the due date.

The table lists eight points on the timeline, each with its date and either "passed" or a count of days still to go. The labels are general guides, and your own care team sets the real appointment schedule.

• 13 weeks: end of the first trimester.
• 20 weeks: the anatomy scan, which the tool says usually falls around 18 to 22 weeks.
• 24 weeks: a viability milestone.
• 28 weeks: the third trimester begins.
• 37 weeks: early term, followed by full term at 39 weeks and the due date at 40.
• 42 weeks: the post-term limit.

Nothing is saved between visits, so note your dates if you want to keep them.