Finding out you are pregnant brings an immediate question: when is the baby due? This due date calculator estimates your due date from the first day of your last period, your conception date or your IVF transfer date. It also tells you how many weeks pregnant you are, which trimester you are in and when key milestones fall.
Quick answer: Due date = first day of last period + 280 days (40 weeks), adjusted for cycle length; or conception + 266 days; or IVF transfer + 261 days (5-day embryo). A last period on March 1, 2026 gives a due date of December 6, 2026.
How to use the due date calculator
- Choose a method: last period, conception date or IVF transfer.
- Enter the date. For the last-period method, add your average cycle length if it is not 28 days.
- Leave Calculate as of on today (or change it to see another date).
- Press Calculate to see your due date, how far along you are, your trimester, days to go and a timeline of milestones.
Due date formulas
| Method | Formula | Example |
|---|---|---|
| Last period (28-day cycle) | LMP + 280 days | Mar 1 → Dec 6, 2026 |
| Last period (other cycle) | LMP + 280 + (cycle − 28) days | 32-day cycle: Mar 1 → Dec 10, 2026 |
| Conception | Conception + 266 days | Mar 15 → Dec 6, 2026 |
| IVF, 5-day embryo | Transfer + 261 days | Mar 20 → Dec 6, 2026 |
| IVF, 3-day embryo | Transfer + 263 days | Mar 18 → Dec 6, 2026 |
Pregnancy timeline by week
| Milestone | Week |
|---|---|
| Missed period, positive home test likely | 4 |
| Heartbeat often visible on ultrasound | 6 |
| End of first trimester | 13 weeks 6 days |
| Anatomy scan window | 18–22 |
| Glucose screening | 24–28 |
| Third trimester begins | 28 |
| Full term begins | 39 |
| Due date | 40 |
| Late term | 41 |
The calculator turns each milestone into a date for your pregnancy.
Example
The first day of the last period was March 1, 2026, cycles are 28 days.
- Due date: March 1 + 280 days = Sunday, December 6, 2026
- On October 3, 2026: 216 days = 30 weeks 6 days, third trimester, 64 days to go
- Estimated conception: about March 15, 2026
- End of the first trimester: June 6, 2026
How to read your result
- Treat it as a window, not a deadline. Most babies arrive between 38 and 42 weeks.
- Your provider may adjust the date after the first ultrasound, especially if your cycles are irregular.
- Planning ahead? If you are trying to conceive, the ovulation calculator shows your fertile window and the due date for each cycle.
- Healthy weight gain depends on your pre-pregnancy weight; check it with the BMI calculator.
- Eating for two? Most people need no extra calories in the first trimester and about 340–450 more a day later on; start from your baseline with the calorie calculator.
- Counting the days? The age calculator gives the exact time between any two dates.
Common mistakes
- Counting from conception instead of the last period. Pregnancy weeks start about two weeks before conception.
- Ignoring cycle length. Long or short cycles move the due date.
- Using the date of a positive test. The test date is not the start of the pregnancy.
This calculator gives an estimate and is not medical advice. Your doctor or midwife will confirm your due date, usually with an ultrasound.
Frequently asked questions
How is a due date calculated?
Doctors count 280 days (40 weeks) from the first day of your last menstrual period. This is called Naegele’s rule. If your cycles are longer or shorter than 28 days, the date shifts by the difference: a 32-day cycle adds 4 days. A last period starting March 1, 2026 gives a due date of December 6, 2026.
How many weeks pregnant am I?
Pregnancy weeks are counted from the first day of your last period, not from conception, so you are already about 2 weeks ‘pregnant’ when you conceive. With a last period on March 1, 2026, on October 3, 2026 you would be 30 weeks and 6 days pregnant, in the third trimester.
How do I calculate my due date from conception?
Add 266 days (38 weeks) to the conception date. Conception on March 15, 2026 gives a due date of December 6, 2026. Most people do not know the exact day of conception, so the last-period method is used more often.
How is an IVF due date calculated?
For a 5-day embryo (blastocyst) transfer, add 261 days to the transfer date; for a 3-day embryo, add 263 days. Because the embryo’s age is known exactly, IVF due dates are the most precise.
What are the trimesters of pregnancy?
The first trimester runs to the end of week 13, the second from week 14 to the end of week 27 and the third from week 28 until birth. A pregnancy is considered full term from 39 weeks 0 days to 40 weeks 6 days.
How accurate is my due date?
It is an estimate. Only about 4% of babies are born on their due date, and most arrive within two weeks either side. An ultrasound in the first trimester, which measures the baby’s size, is the most accurate way to confirm the date.
When will I find out I am pregnant?
Most home pregnancy tests detect pregnancy from the first day of your missed period, around 4 weeks after the start of your last period. Testing earlier can give a false negative.
Can my due date change?
Yes. If an early ultrasound measurement differs from your last-period date by more than about a week, your provider may change your due date to match the scan. After that, the date normally stays the same.
Last updated: