Pregnancy Due Date Calculator
Estimate your baby's due date and track your pregnancy milestones
Due Date Calculator
Estimated Due Date: —
Key Milestones
Frequently Asked Questions
How is the due date calculated?
The standard method (Naegele's rule) adds 280 days (40 weeks) to the first day of your last menstrual period (LMP).
How accurate is the estimated due date?
Only about 5% of babies are born exactly on their due date. Most births occur within 2 weeks before or after the EDD.
What trimester am I in?
First trimester: weeks 1–12. Second trimester: weeks 13–26. Third trimester: weeks 27–40.
About this calculator
The Pregnancy Due Date Calculator estimates your baby's due date from the first day of your last menstrual period, and lists the milestones along the way: the end of the first trimester, the anatomy scan at about 20 weeks, the end of the second trimester and the start of early term at 37 weeks.
It uses Naegele's rule, which adds 280 days, or 40 weeks, to the first day of your last period, with an adjustment if your cycle is longer or shorter than 28 days. Only about 4 to 5 percent of babies arrive on the due date. Think of it as the middle of a window of a few weeks, and let your doctor confirm it with an ultrasound.
How to use it
- Enter the first day of your Last Menstrual Period.
- Enter your usual Cycle Length in days. 28 is the default.
- Press Calculate Due Date.
- Read the due date and the milestone dates.
Naegele's rule
Due date = LMP + 280 days, adjusted by Cycle length − 28 days. Gestational age is counted from the first day of the last period, not from conception, which is why a pregnancy is called 40 weeks long even though conception happens about two weeks after the LMP.
Worked example
Last period began 1 January 2026, 28-day cycle
| Estimated due date | 8 October 2026 |
| End of first trimester | 26 March 2026 |
| Anatomy scan (about 20 weeks) | 21 May 2026 |
| End of second trimester | 2 July 2026 |
| Early term begins (37 weeks) | 17 September 2026 |
A due date from an early ultrasound is more reliable than one based on the LMP when the two differ by more than a week.
Tips and common mistakes
- This is an estimate. Your doctor may adjust the date after an early ultrasound.
- If your cycle is irregular, tell your doctor. The LMP method is less accurate then.
- Doctors now describe 37 to 38 weeks as early term, 39 to 40 weeks as full term and 41 weeks as late term, so a baby born in the 39 to 40 week window is considered full term.
- Use the milestone dates to book scans and antenatal checks in advance.
- This tool is for information and does not replace medical advice.
Frequently asked questions
How is the due date calculated?
Naegele's rule adds 280 days to the first day of your last menstrual period.
How accurate is the due date?
Only about 4 to 5 percent of babies are born on the due date. Most arrive within two weeks either side.
What if my cycle is not 28 days?
The date is adjusted by the difference between your cycle length and 28 days.
When is the anatomy scan?
Around 18 to 22 weeks, often at about 20 weeks.
What is full term?
Full term is 39 weeks to 40 weeks and 6 days. Early term is 37 to 38 weeks, late term 41 weeks, and after 42 weeks is post-term.
Can I use it for IVF?
IVF due dates are calculated from the embryo transfer or egg retrieval date, so confirm the date with your clinic.