Due date and pregnancy week calculator
Your due date is 280 days (40 weeks) after the first day of your last period. Enter a date and the calculator shows your due date, current pregnancy week, trimester and key dates.
Key dates
Save your due date in the app
Calm Parent counts your pregnancy week every day and has a contraction timer. After the birth, one tap turns it into a baby log.
Get it on Google PlayHow the due date is calculated
Doctors count pregnancy from the first day of your last period, not from conception. The due date is that day plus 280 days, or 40 weeks (Naegele’s rule). If your cycle is longer or shorter than 28 days, the due date moves by the difference.
An ultrasound due date is more accurate
An ultrasound in the first trimester gives the most accurate due date. If your doctor set your due date from a scan, choose “ultrasound due date” and the calculator will work out your pregnancy week from it.
Few babies arrive exactly on the due date
The due date is an estimate. A pregnancy is full term from 37 weeks, and a birth between 37 and 42 completed weeks counts as on time. That’s why it’s worth having your hospital bag ready by about 36 weeks.
Frequently asked questions
When does pregnancy week counting start?
From the first day of your last period. That’s why at conception you are already about 3 weeks pregnant.
What does 24w 3d mean?
24 full weeks and 3 days. You are then in week 25 of pregnancy.
How long is each trimester?
The first trimester lasts until the end of week 13 (13w 6d), the second until the end of week 27 (27w 6d), and the third from week 28 until birth.
Sources
- ACOG Committee Opinion No. 700: Methods for Estimating the Due Date (2017)
- WHO: Preterm birth, definitions of preterm and term birth (2023)
This article is for information only and does not replace medical advice. If something worries you, contact a doctor. In an emergency, call your local emergency number.