Calculate your due date and how many weeks pregnant you are
Enter the first day of your last period or your conception date: your estimated due date, how far along you are and the key dates appear. An estimate calculated in your browser; nothing is sent.
- 40-week or 41-week term
- Weeks pregnant
- Key dates calendar
- Nothing is sent
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How do you calculate your due date?
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Choose the method
The first day of your last menstrual period (LMP), with your usual cycle length (28 days by default), or your conception date if you know it.
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Choose the convention
40 weeks, Naegele's rule used in most countries, or 41 weeks, the convention used in France.
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Read the results
Estimated due date, weeks pregnant, weeks since conception, month, trimester, days to go and a calendar of key dates.
All your pregnancy milestones in one place
Last period or conception
Two ways to calculate, with a cycle length from 21 to 45 days to adjust the estimate when your cycle isn't 28 days.
Weeks and days
How far along you are today in weeks and days since your last period (for example 12w 3d), in weeks since conception, in months and in trimesters.
Key dates calendar
End of the 1st trimester (14 weeks), start of the 3rd (28 weeks), baby considered term (37 weeks), due date and 42 weeks.
Progress and days to go
A progress bar, the number of days until your due date and the estimated conception date.
How is your due date calculated?
The calculation starts from the first day of your last menstrual period (LMP). Naegele's rule, used by doctors and midwives in most countries, adds 40 weeks, or 280 days, to that date. France uses a 41-week term instead, or 287 days, which the calculator offers as an option. Example: if your last period started on January 5, 2026, your due date is October 12, 2026 at 40 weeks and October 19, 2026 at 41 weeks. These dates assume a 28-day cycle with ovulation around day 14. If your cycle lasts 32 days, you probably ovulated later, so the estimate moves 4 days later, to October 16, 2026. If you know your conception date, your due date is 266 days after it.
Weeks pregnant, weeks since conception and trimesters
Pregnancy is counted in weeks from the first day of your last period, not from conception, which usually happens about two weeks later. So when you are 12 weeks pregnant, the embryo is about 10 weeks old. The first trimester lasts until 14 weeks, the second until 28 weeks and the third runs from 28 weeks to birth. A baby is considered term from 37 weeks; doctors in the US further distinguish early term (37 to 38 weeks), full term (39 to 40 weeks) and late term (41 weeks), and a pregnancy that goes beyond 42 weeks is called post-term. With a last period on January 5, 2026, 14 weeks falls on April 13, 28 weeks on July 20, 37 weeks on September 21 and 42 weeks on October 26, 2026.
An estimate, not a diagnosis
This calculator gives an approximate date. Cycles vary, ovulation doesn't always happen at the same time and the date of your last period isn't always certain. In practice, a first-trimester ultrasound, often called the dating scan, lets your doctor or midwife confirm or adjust your due date from the size of the baby. Only a small share of babies are born on their exact due date: most arrive in the weeks around it. This calculation does not replace your prenatal care with a midwife, doctor or obstetrician. For any question about your health or your baby's, please ask them.
Frequently Asked Questions
How do I calculate my due date?
Add 280 days (40 weeks) to the first day of your last period: this is Naegele's rule. An early ultrasound in the first trimester can then confirm or adjust the date.
Why is the due date 40 weeks, and why 41 weeks in France?
It's a matter of convention. Most countries use Naegele's rule, 40 weeks or 280 days after the last period, while France sets the term at 41 weeks, or 287 days. The two dates are one week apart.
What's the difference between weeks pregnant and weeks since conception?
Weeks pregnant (gestational age) are counted from your last period; weeks since conception (fetal age) start about two weeks later. Just subtract 2: at 20 weeks pregnant, the baby is about 18 weeks old.
How accurate is the calculated due date?
It's an estimate that depends on how regular your cycle is and on the date of your last period. The due date used for your care is the one your doctor or midwife confirms, usually with the first-trimester ultrasound.
When is a baby considered full term?
A baby is considered term from 37 weeks. Birth before 37 weeks is called preterm, and a pregnancy beyond 42 weeks is post-term. Your midwife or doctor will tell you what monitoring is planned as your due date approaches.