Pregnancy Calculator
Find out how many weeks pregnant you are and your estimated due date. Use your last period, conception date, an ultrasound or an IVF transfer, and see every key date on one timeline.
Key dates
This calculator is for information only and does not replace medical advice. Your doctor or midwife will confirm your due date, usually with an early ultrasound.
How to use the pregnancy calculator
- Choose what you know: Last period, Conception, Ultrasound, IVF transfer or Due date.
- Pick the date. For the last-period method, change the cycle length if your cycle is usually shorter or longer than 28 days.
- For an ultrasound, enter the scan date and the age it showed (for example 8 weeks 3 days). For IVF, choose whether a day 3 or day 5 embryo was transferred.
- You instantly see how many weeks and days pregnant you are, your due date, the trimester and a timeline of key dates and tests.
- Want to know how far along you will be on a certain day? Open Calculation date and choose that day.
How is the due date calculated?
Pregnancy is counted from the first day of your last menstrual period (LMP), not from conception. That is why you are already considered “2 weeks pregnant” at the moment of conception, and why a full-term pregnancy is 40 weeks (280 days) long even though the baby grows for about 38 weeks. Doctors write pregnancy age as weeks + days: 12+3 means 12 full weeks and 3 days, so you are in your 13th week.
Naegele’s rule
Due date = first day of last period + 280 days
Shortcut: + 1 year − 3 months + 7 days
The rule assumes a 28-day cycle with ovulation on day 14. If your cycles are longer, you probably ovulated later, so the due date moves later by the same number of days; a 32-day cycle adds 4 days. For example, if your last period started 70 days ago, you are 10 weeks pregnant today. Try it in the calculator.
Other methods
| If you know | Due date |
|---|---|
| Conception date | + 266 days |
| Ultrasound (age on the scan) | scan date + 280 days − scan age |
| IVF, day 5 blastocyst transfer | + 261 days |
| IVF, day 3 embryo transfer | + 263 days |
An early ultrasound is the most accurate way to date a pregnancy, because in the first trimester all babies grow at almost the same rate. If the scan and your last period disagree by more than a few days, your doctor will usually go by the scan. With IVF the dates are known exactly, so the transfer date gives the most precise estimate. Example: a scan two weeks ago showed 9+2.
Trimesters
Pregnancy is divided into three trimesters. The first trimester (weeks 1–13) is when the organs form and screening tests begin. The second trimester (weeks 14–27) is often the most comfortable; you usually feel the first movements and have the detailed anatomy scan. The third trimester (week 28 to birth) is about growth and getting ready for delivery.
Only about 1 in 20 babies is born on the exact due date. A birth between 37 and 42 weeks is considered normal, so think of the due date as the middle of a window rather than a deadline. Test timings in the timeline are typical ranges; your care team may schedule them differently. Everything is calculated in your browser and nothing you enter is sent anywhere.
Frequently asked questions
How many weeks pregnant am I?
Count the days since the first day of your last period and divide by 7. The full weeks are your pregnancy week and the rest are days; 75 days is 10 weeks 5 days (10+5), which means you are in week 11. The calculator above does this for you.
How accurate is the due date?
It is an estimate. Only about 4–5% of babies arrive on their due date, and most are born between 38 and 42 weeks. An early ultrasound or an IVF transfer date gives the most accurate estimate.
My ultrasound gives a different date. Which one is right?
If the difference is more than a few days, doctors usually trust a first-trimester ultrasound, because babies grow at very similar rates early on. Use the Ultrasound option with the age shown on your scan.
How do I calculate the due date after IVF?
Add 261 days to the transfer date for a day 5 blastocyst, or 263 days for a day 3 embryo. Choose IVF transfer above and select the embryo age.
How many months pregnant am I?
Pregnancy is about 9 months long. Months 1–3 cover weeks 1–13, months 4–6 weeks 14–27 and months 7–9 weeks 28–40. The table next to the calculator shows each month and highlights where you are.