Expecting a baby? This free calculator estimates your due date from the first day of your last period or from your conception date. It also shows how many weeks pregnant you are today, how long is left and the dates of each trimester. Nothing you enter leaves your device.
How your due date is calculated
Doctors and midwives count a pregnancy as 40 weeks (280 days) from the first day of your last menstrual period. Naegele’s rule is the standard method: due date = first day of last period + 280 days. It assumes a 28-day cycle. If your cycle is longer or shorter, the calculator adjusts the date by the difference, so a 32-day cycle adds 4 days and a 24-day cycle takes away 4.
If you know the day you conceived, the calculator adds 266 days (38 weeks) instead. This is why a pregnancy is “40 weeks” in total even though the baby has been growing for about 38 weeks. Dates for in vitro fertilization (IVF) are counted from the transfer date and the age of the embryo, so ask your clinic for your date.
The three trimesters
| Stage | Weeks of pregnancy | What it covers |
|---|---|---|
| First trimester | Up to 13 weeks 6 days | Early development; many people feel tired or sick |
| Second trimester | 14 to 27 weeks 6 days | Growth and movements; energy often returns |
| Third trimester | 28 weeks until birth | Final growth and preparing for birth |
How reliable is a due date?
- It is an estimate. Only about 5% of babies are born on their due date. Most arrive in the weeks around it, and a baby is considered full term from 37 weeks.
- An early ultrasound is the most accurate. If a scan in the first trimester differs from the calculator, your midwife or doctor will usually use the scan date.
- Irregular cycles make a last-period date less certain. Tell your midwife or doctor.
Please confirm your date with your midwife or doctor. This tool is only for estimating a due date. It is not for contraception, and it cannot predict fertility or the best days to conceive.
Healthy habits during pregnancy
Book your first antenatal appointment as early as you can, and ask your midwife or doctor about vitamins, food safety and exercise that suit you. Good sleep helps: see our 8 sleep habits. Gentle daily movement such as walking is often suggested (read our walking guide and check with your care team), and fiber helps with digestion: the fiber guide. Our other calculators, such as the calorie and weight loss tools, are not designed for pregnancy.
Contact your midwife or doctor urgently if…
- You have bleeding, severe or constant pain, or fluid leaking.
- You notice your baby moving much less than usual.
- You have a severe headache, vision changes or sudden swelling of your face or hands.
Frequently asked questions
How accurate is a due date calculator?
It gives a good estimate, but only about 5% of babies are born on the exact date. Most are born within a couple of weeks either side. An early ultrasound is the most accurate way to date a pregnancy.
How is the due date calculated from the last period?
The calculator adds 280 days to the first day of your last period. If your cycle is not 28 days, it adjusts by the difference, which is how Naegele’s rule is commonly applied.
What if I do not know my last period date?
Use the conception date if you know it, or ask your midwife or doctor for an ultrasound scan, which can estimate the date.
Is it OK to use this calculator to plan a pregnancy?
No. This tool only estimates a due date after conception. It cannot tell you when you are fertile and is not a method of contraception.
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This calculator provides general estimates for healthy adults and is for information only. It is not medical advice and does not replace a conversation with a qualified healthcare professional. Read our disclaimer and editorial policy.