Due Date Calculator: When Is My Baby Due?
This due date calculator estimates when your baby is due and how far along you are today. Enter the first day of your last period, the date of conception or your IVF embryo transfer date, and see your estimated due date, current week of pregnancy, trimester and key milestones.
| Milestone | Week | Date |
|---|
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Quick answer: Your due date is usually 280 days (40 weeks) after the first day of your last menstrual period, or 266 days after conception. The calculator adjusts this if your cycles are longer or shorter than 28 days.
How to use the due date calculator
- Choose what you know: the first day of your last period, the conception date, or an IVF transfer date for a day 3 or day 5 embryo.
- Pick the date. If you use your last period, enter your average cycle length too.
- Read your estimated due date, how many weeks and days pregnant you are today, your trimester and the days to go.
- Check the milestones table for the dates of key scans and stages.
How the due date is calculated
Doctors and midwives use Naegele’s rule: add one year, subtract three months and add seven days to the first day of your last period. That is the same as adding 280 days. Pregnancy is counted from the start of the last period, about two weeks before conception, which is why you are already “4 weeks pregnant” around the time a test turns positive.
- Longer or shorter cycles: ovulation shifts, so the due date moves by the difference from 28 days.
- Conception date: due date = conception + 266 days.
- IVF: due date = transfer date + 263 days for a day 3 embryo, or + 261 days for a day 5 blastocyst.
Trimesters
| Trimester | Weeks |
|---|---|
| First | Week 1 to the end of week 13 |
| Second | Week 14 to the end of week 27 |
| Third | Week 28 until birth |
Is the due date exact?
No. It is an estimate. Only about 4 percent of babies are born on their due date, and a birth anywhere from 37 to 42 weeks is considered normal. An early ultrasound, especially between 8 and 13 weeks, measures the baby and is often used to confirm or adjust the date.
This tool is for information only and does not replace advice from your doctor or midwife. Count the days with the countdown timer, or work out exact dates with days between dates.
FAQ
How many weeks pregnant am I?
The “Weeks pregnant today” box shows it in weeks and days, counted from your last period.
What if I don’t know my last period date?
Use the conception date if you know it, or ask for a dating scan. An early ultrasound gives the most reliable estimate.