Pregnancy Due Date Calculator
Estimate your pregnancy due date, current gestational age, and trimester from your last menstrual period, instantly in your browser.
How to use the Pregnancy Due Date Calculator
- Enter the first day of your last menstrual period (LMP).
- Optionally enter your average cycle length if it isn't 28 days.
- Click Run to see your estimated due date, current gestational age in weeks and days, and trimester.
How the Pregnancy Due Date Calculator works
The calculator uses Naegele's rule: a pregnancy is dated as 280 days (40 weeks) from the first day of the last menstrual period. If your cycle is longer or shorter than 28 days, the due date is shifted by the difference, since ovulation happens later or earlier in the cycle.
Gestational age is counted from the LMP, so it is about two weeks more than the time since conception. The calculator treats weeks 0 to 12 as the first trimester, weeks 13 to 26 as the second and week 27 onwards as the third. Only around 5% of babies arrive on their due date; your midwife or doctor may adjust it after an ultrasound scan.
Frequently asked questions
- Is this pregnancy due date calculator free?
- Yes. Estimate your due date at no cost, with no account required.
- How is the due date calculated?
- Using Naegele's rule: 280 days (40 weeks) are added to the first day of your last menstrual period, adjusted for cycle lengths other than 28 days.
- Is this an exact due date?
- No. This is an estimate. Only about 5% of babies are born on their exact due date. Consult your healthcare provider for a medical estimate.