Pregnancy Due Date Calculator
Enter the first day of your last period and your usual cycle length. You get your estimated due date, how far along you are today, and when the main scans and tests usually happen.
Your dates
From the first day of one period to the day before the next.
Worked out in your browser; your dates are not stored. A share link puts them in the web address.
Your estimated due date
pregnant today
These dates start in the future, so there are no weeks to count yet.
This due date was more than two weeks ago.
- Estimated conception
- Second trimester starts
- Third trimester starts
- Most babies arrive (37–42 weeks)
Enter a date to see your due date.
Your pregnancy timeline
Typical timings from ACOG, NHS, and CDC guidance, last checked 16 October 2026. Your midwife or doctor will tell you what applies to you. This calculator gives estimates, not medical advice.
About the Pregnancy Due Date Calculator
The due date calculator estimates when your baby is due and how far along you are. Start from your last period, the day you conceived, an IVF transfer, or an ultrasound scan. It also shows your trimester, the days to go, and when the usual scans and tests happen. Your dates are worked out in your browser and never stored.
How to use it
- 1 Pick how you want to date the pregnancy: last period, conception, IVF transfer, or ultrasound.
- 2 Enter the date, plus your cycle length, embryo age, or the scan result.
- 3 Read your due date, how many weeks pregnant you are today, and your trimester.
- 4 Check the timeline for scan and test dates, and copy the share link if you like.
Frequently asked questions
How is a due date calculated?
The usual method, Naegele’s rule, adds 280 days (40 weeks) to the first day of your last period. That assumes a 28-day cycle; with a longer or shorter cycle the date moves by the difference, so a 32-day cycle adds four days.
Why are pregnancy weeks counted from my last period?
Most people know the date of their last period but not the day they conceived. So pregnancy is dated from the period, about two weeks before conception. At conception you are already counted as about two weeks pregnant.
How accurate is my due date?
It is an estimate. Only about 1 in 25 babies arrive on their due date, and most are born between 37 and 42 weeks. A scan in the first trimester is the most accurate way to date a pregnancy, and your doctor or midwife may change the date after it.
How do I calculate my IVF due date?
Add 266 days to the egg retrieval date, then take away the embryo’s age at transfer. So a day 5 blastocyst transfer gives a due date 261 days after the transfer, and a day 3 transfer gives 263 days.
What are the trimesters?
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.
Can I find out when I conceived from my due date?
Roughly. Conception is usually about 266 days (38 weeks) before the due date. Sperm can live up to five days, so the intercourse that led to the pregnancy may have been a few days before that.