Pregnancy Due Date Calculator
Estimate your due date from your last period, conception date or IVF transfer date. See how many weeks pregnant you are, your trimester and key dates.
Only about 1 in 25 babies arrives on the due date itself; most are born within two weeks either side. An early ultrasound gives the most accurate date, so follow your midwife or doctor.
How due dates are worked out
Doctors count pregnancy from the first day of your last menstrual period (LMP), about two weeks before conception, and estimate the due date as 280 days (40 weeks) later. This is Naegele's rule. If your cycle is longer or shorter than 28 days, ovulation shifts too, so the calculator adjusts the date by the difference. You can also start from a known conception date or an IVF embryo transfer date (day 3 or day 5). The result shows how far along you are today, your trimester, and when each trimester ends.
How to use it
- 1
Choose a starting point
Your last period, conception date, or IVF transfer date.
- 2
Enter the date
For your last period, also enter your usual cycle length.
- 3
See your due date
Along with weeks pregnant, trimester and key milestones.
Frequently asked questions
How accurate is the due date?
It's an estimate: only about 4% of babies arrive on their due date, and most come within two weeks either side. A dating ultrasound in the first trimester is the most accurate method.
Why are there two weeks of pregnancy before conception?
Because pregnancy is counted from the last period, which is easier to know than the day of conception. At conception you're already considered two weeks pregnant.
When does each trimester start?
The first trimester runs to the end of week 13, the second from week 14 to the end of week 27, and the third from week 28 to birth.
Is anything sent to a server?
No. Everything is calculated in your browser, and nothing you type is stored or sent anywhere.