Due Date Calculator
Free pregnancy due date calculator. Estimate your due date from the first day of your last period, and see how many weeks pregnant you are and which trimester you're in.
How your due date is estimated
This calculator uses Naegele’s rule: it counts 280 days (40 weeks) from the first day of your last menstrual period (LMP), adjusted slightly if your cycle is longer or shorter than the typical 28 days. Pregnancy is measured from the LMP, so by the time most people learn they’re pregnant they’re already a few weeks along.
An estimate, not a guarantee
Only about 1 in 20 babies arrive exactly on their due date — most come within a couple of weeks either side. An ultrasound dating scan gives a more precise estimate. Always confirm with your doctor or midwife; this tool is for general information only.
Frequently asked questions
How is my due date calculated?⌄
Using Naegele's rule: 280 days (40 weeks) from the first day of your last menstrual period, adjusted for your cycle length.
How accurate is a due date?⌄
It's an estimate — only about 1 in 20 babies arrive exactly on their due date, and most come within two weeks either side. An ultrasound scan is more precise.
How many weeks pregnant am I?⌄
Pregnancy is counted from the first day of your last period, so enter that date and the calculator shows your current week and trimester.
Have another question? Get in touch.