Find your estimated due date and how far along you are. Enter the first day of your last menstrual period to see your due date, current week and trimester.
This is an estimate only. Your doctor will confirm your due date, usually with an ultrasound scan. Only about 5 percent of babies are born exactly on their due date.
1. Select the first day of your last menstrual period from the calendar. 2. Click Calculate Due Date. 3. Read your estimated due date, your current week and your trimester.
When you find out you are pregnant, the first question is usually: when is the baby due? This free pregnancy due date calculator gives you the answer in seconds. Enter the first day of your last menstrual period (LMP), and it shows your estimated due date, how many weeks pregnant you are, and which trimester you are in. Doctors use the same method, called Naegele's rule, to work out the due date at your first appointment.
A normal pregnancy lasts about 40 weeks, or 280 days, counted from the first day of the last period — even though conception usually happens about two weeks later. That is why your pregnancy is counted as 40 weeks even though the baby has been growing for about 38 weeks. Only about 5 percent of babies arrive exactly on their due date; most are born within two weeks before or after it, and that is completely normal.
Suppose the first day of your last period was 1 January 2026. Add 280 days (40 weeks) to that date, and the estimated due date is 8 October 2026. Conception probably happened around 15 January 2026, about two weeks after the last period started. If today is 10 March 2026, you are about 9 weeks and 6 days pregnant, in your first trimester. Try it in the calculator above: enter 1 January 2026 as the last period date and check that your result matches.
Take another date: the first day of the last period was 15 June 2026. Add 280 days and the due date is 22 March 2027. Conception was probably around 29 June 2026. If today is 1 September 2026, you are about 11 weeks pregnant and still in the first trimester. The second trimester starts at week 14, which would be around 14 September 2026, and the third trimester starts at week 28, around 21 December 2026. Enter 15 June 2026 in the calculator and check the due date of 22 March 2027.
The calculation uses Naegele's rule: due date = first day of the last menstrual period + 280 days (40 weeks). Your current week is the number of full weeks since the last period, plus one, because the first week of pregnancy is counted from the last period even before conception. The three trimesters are: first trimester, weeks 1 to 13; second trimester, weeks 14 to 27; and third trimester, weeks 28 to 40. Your doctor may adjust the due date after an early ultrasound scan, which measures the baby directly and is more accurate than the last period date.
Use the first day, not the last day, of your period. The calculation starts from the first day of bleeding. Check your cycle length. The 280-day rule assumes a 28-day cycle; if your cycles are much longer or shorter, your doctor will adjust the date. Remember the date is an estimate. Only about 1 in 20 babies is born on the exact due date. Book your first antenatal visit early. See a doctor as soon as you know you are pregnant, ideally before week 10. Take folic acid. Doctors recommend folic acid from before conception and through the first 12 weeks.
Using the last day of your period. The count starts from the first day of bleeding, not the last. Counting from the date of conception. Doctors count pregnancy from the last period, which is about two weeks before conception. Expecting the baby on the exact date. The due date is an estimate; most babies arrive within two weeks either side of it. Forgetting irregular cycles. If your periods are irregular, the last period date is less reliable and an ultrasound is more accurate. Skipping antenatal care. A due date calculator cannot replace a doctor, who checks your health and the baby's growth.
Pro Tip: Write down your due date and your trimester dates in your phone, and set a reminder for your antenatal appointments — they are usually every 4 weeks at first, then more often near the end.
Note: This calculator gives an estimate only and is not medical advice. Always see a doctor or midwife for your pregnancy care, and follow their guidance.
How is a due date calculated? The due date is the first day of your last menstrual period plus 280 days (40 weeks). This is called Naegele's rule, and doctors use the same method.
How many weeks is a normal pregnancy? A normal pregnancy lasts about 40 weeks from the first day of the last period. A baby born between 37 and 42 weeks is considered full term.
What if I do not know my last period date? If you do not know the date, or your periods are irregular, an early ultrasound scan can measure the baby and estimate the due date more accurately. Ask your doctor.
Is the due date the exact day the baby will be born? No. Only about 5 percent of babies are born on their due date. Most are born within two weeks before or after it, and that is completely normal.
What are the three trimesters? The first trimester is weeks 1 to 13, the second is weeks 14 to 27, and the third is weeks 28 to 40. Each trimester has different symptoms and check-ups.
When should I see a doctor after a positive test? As soon as possible, ideally before week 10. Early antenatal care checks your health, confirms the due date and starts folic acid and other care.
Does the due date change? Yes, it can. An early ultrasound may move the due date by a few days if the baby measures bigger or smaller than expected. Your doctor will tell you the final date.
Can I use this calculator if my cycles are irregular? You can, but the result is less reliable. With irregular cycles, an ultrasound scan gives a better estimate than the last period date.