Due Date Calculator
Estimate your baby's due date from the first day of your last period, plus how far along you are and your current trimester.
Enter the first day of your last menstrual period to estimate your due date.
How to use this calculator
Enter the first day of your last menstrual period and your average cycle length. The calculator estimates your due date, how many weeks and days along you are, and your current trimester.
How due dates work
Pregnancy is counted from the first day of your last period, not from conception, because that date is easier to pin down. Full term is 40 weeks (280 days) from that day. Since ovulation depends on cycle length, the estimate is adjusted when your cycle differs from 28 days.
Worked example
If your last period began on a given date and your cycle is 28 days, your estimated due date is exactly 280 days later. A 32-day cycle pushes the estimate about four days later.
This is an estimate, not medical advice. Your healthcare provider and a dating ultrasound give the most reliable due date.
Frequently asked questions
How is my due date calculated?
The standard method (Naegele's rule) adds 280 days — 40 weeks — to the first day of your last menstrual period. This calculator also adjusts for cycle lengths other than 28 days.
How accurate is the due date?
It's an estimate. Only about 1 in 20 babies arrive on the exact due date; most are born within two weeks either side. An early dating ultrasound is the most accurate method.
What if my cycle isn't 28 days?
Ovulation timing shifts with cycle length, so the calculator adds or subtracts the difference from 28 days to refine the estimate.
What are the trimesters?
Pregnancy is divided into three trimesters: the first through about week 13, the second from weeks 14–27, and the third from week 28 to birth.