Due Date Calculator
Pregnancy due date & trimester timeline.
About this calculator
One of the first questions after a positive test is “when is the baby coming?” Doctors estimate the due date as 40 weeks (280 days) from the first day of the last menstrual period. Our calculator gives you that date instantly, plus the full trimester timeline so you know what stage you are in right now.
The timeline also helps you plan — when to book checkups, when maternity leave conversations start, and what to expect in each trimester. Enter the first day of your last period (and average cycle length if you know it) for a personalised estimate. Only about 5% of babies arrive exactly on the due date, so treat it as a guide, not an appointment.
How to use
- Enter the first day of your last menstrual period.
- Add your average cycle length (default 28 days) if you know it.
- Get your estimated due date and current week of pregnancy.
- Follow the trimester timeline and confirm everything with your doctor’s ultrasound.
Frequently asked questions
How is the due date calculated?
Doctors add 280 days (40 weeks) to the first day of your last menstrual period — this is Naegele’s rule, adjusted if your cycle differs from 28 days.
How accurate is a due date calculator?
It’s an estimate — only about 1 in 20 babies is born on the exact due date. An early ultrasound gives a more precise dating.
What are the three trimesters?
First: weeks 1–13, second: weeks 14–27, third: weeks 28–40. The calculator shows which trimester you’re in and the key milestones of each.
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