Pregnancy Due Date Calculator
This pregnancy due date calculator estimates your due date with Naegele's rule — 280 days from the first day of your last menstrual period, or 266 days from conception — and shows how many weeks pregnant you are, your trimester and the days remaining.
About this tool
This pregnancy due date calculator estimates your due date with Naegele's rule — 280 days from the first day of your last menstrual period, or 266 days from conception — and shows how many weeks pregnant you are, your trimester and the days remaining.
How to use it
- Choose whether to calculate from your last menstrual period (LMP) or the conception / IVF transfer date.
- Enter the date.
- Read your estimated due date, current week and day of pregnancy, trimester and days left.
Good to know
- Naegele's rule: due date = first day of the last menstrual period + 280 days (40 weeks).
- From a conception date, the calculator adds 266 days (38 weeks).
- Pregnancy weeks are counted from the LMP, which is about two weeks before conception.
- Trimesters: first until week 13, second weeks 13–26, third from week 27.
- Only about 5% of babies are born on their exact due date; most arrive within about two weeks of it.
Runs entirely in your browser — nothing you enter is uploaded or stored.
Frequently asked questions
How is a due date calculated?
The standard method, Naegele's rule, adds 280 days to the first day of your last menstrual period. Your care provider may adjust the date after an early ultrasound, which is usually more accurate.
What if my cycle is not 28 days?
Naegele's rule assumes a 28-day cycle with ovulation around day 14. With longer or irregular cycles the estimate can be off, and an ultrasound gives a better date.
How many weeks pregnant am I?
Pregnancy is counted from the first day of your last period, so at conception you are already considered about two weeks pregnant. The calculator shows your current week and day.
How accurate is a due date?
It is an estimate: only about 5% of babies are born on their due date, and a full-term birth anywhere from about 37 to 42 weeks is normal. Always follow your midwife's or doctor's guidance.