Due Date Calculator
Guide: How Pregnancy Due Dates Are Calculated
Nothing you enter or choose here leaves your device. This tool runs in your browser.
How to use
- 1Choose whether to use your last period or the conception date.
- 2Pick the date, and adjust your cycle length if it isn't 28 days.
- 3Read your due date, how far along you are, and the key dates.
Frequently asked questions
How is the due date calculated?
By adding 280 days (40 weeks) to the first day of your last period. If you know the conception date, 266 days are added to that instead.
What if my cycle isn't 28 days?
Enter your usual cycle length. A longer cycle moves the due date later, and a shorter one moves it earlier.
How accurate is a due date?
It is an estimate. Only about 5 in 100 babies arrive on the due date. A scan or your midwife or doctor can give a more accurate date.
When does each trimester start?
The second trimester starts at week 14 and the third at week 28. A baby is considered term from week 37, and many doctors call weeks 39 to 40 full term.
Is my data sent anywhere?
No. Everything is worked out in your browser and nothing is sent to us.
Read the guide
Learn how this works and how to get the most from it.
Money, health & time
How Pregnancy Due Dates Are Calculated
How a due date is worked out from the last period or conception, how cycle length changes it, and what the weeks and trimesters mean.
1 min read
Related tools
Date Calculator
Count the days between dates or add and subtract time from a date.
Age Calculator
Find your exact age in years, months and days, and your next birthday.
BMI Calculator
Calculate your body mass index and see your healthy weight range.
Calorie Calculator (TDEE)
Estimate daily calories to maintain, lose or gain weight.