About this tool
This calculator uses Naegele's rule: the estimated due date is the first day of your last period plus 280 days, which is 40 weeks. Gestational age is counted from that same first day, so you are 'week 10 and 3 days' when 73 days have passed. For example, a last period starting on 2026-01-01 gives a due date of 2026-10-08, and on 2026-03-12 you would be at 10 weeks 0 days. Pregnancy is split into three trimesters: weeks 0 to 13, weeks 14 to 27 and week 28 until birth. If you only know your due date, choose that option and the start of the count is worked out backwards. A table lists the weeks when common check-ups such as the first ultrasound, screening tests, a detailed ultrasound and the diabetes test usually take place. These are general guides only: your hospital sets the real schedule, and ultrasound measurements can change the due date. This is not medical advice and does not replace your doctor. Nothing you enter is saved or sent.
How to use
- Choose whether you know your last period date or your due date.
- Pick the date.
- Read the due date, the current week and day, and the trimester.
- Check the general table of check-up times and ask your hospital for your real schedule.