Pregnancy Due Date Calculator
Calculate your estimated due date from LMP, conception, or IVF transfer.
Written by Anil Gautam · Updated
How is the due date calculated?
With the LMP method the tool applies Naegele's rule: 280 days, or 40 weeks, after the first day of your last menstrual period. The rule assumes a 28-day cycle, so the tool adds or subtracts the difference when you set another length on the cycle slider, which runs from 21 to 35 days and appears only for this method. A last period starting on 1 January 2026 gives a due date of 8 October 2026 with a 28-day cycle and 12 October 2026 with a 32-day cycle. The hand method of adding a year, subtracting three months and adding seven days gives the same 8 October here, though depending on the months it can land up to three days after the 280-day count.
For the conception method the tool adds 266 days, or 38 weeks, to the date you enter, so a conception date of 15 January 2026 also leads to 8 October 2026. Whichever method you use, the tool works back 266 days from the due date to show an estimated conception date, which for the LMP example is that same 15 January.
Why is a pregnancy counted from the last period?
Pregnancy is dated from the first day of the last period, about two weeks before conception in a 28-day cycle, because that day is usually known and conception usually is not. The current week shown here follows the same convention: it is a gestational age that includes the two weeks before the estimated conception. Setting a longer cycle moves the due date later and makes the week counter read younger by the same number of days.
Trimesters follow those weeks. The tool shows the first trimester until 12w 6d, the second from 13w 0d to 26w 6d, and the third from 27w 0d. Once the due date has passed, the days-to-go line turns into days overdue, and an LMP date in the future keeps the week counter at 0w 0d.
Can you use it for an IVF pregnancy?
Choose the IVF option and enter the transfer date of a day-5 embryo; the tool dates the pregnancy from that transfer. There is no option for a day-3 transfer. Clinics date IVF pregnancies from the embryo's age and the transfer date, so if your clinic gives a different due date, go by the clinic. To count forward from any date, for example to find the date 12 weeks after your last period, the Add or Subtract Days from Date tool does the arithmetic.