Enter the first day of your last period (or your conception date) to estimate your due date, how many weeks along you are and which trimester you're in — instantly.
Estimates only. Most babies arrive within two weeks either side of the due date. Always confirm with your midwife or doctor.
This tool estimates your estimated due date (EDD) — the day around which your baby is most likely to be born — and tells you how far along you are right now in weeks and days, plus which trimester you're in. It works from either the first day of your last menstrual period (LMP) or your conception date, and it adjusts for cycle lengths that differ from the textbook 28 days. Everything updates the moment you change a value, so you can compare scenarios without reloading.
Pregnancy is counted in 40 weeks from the first day of your last period, which is roughly two weeks before you actually conceived. That convention sounds odd, but it's used worldwide because the period date is far easier to pin down than the exact moment of conception. A full-term pregnancy is anything from 37 to 42 weeks, and only about 1 in 20 babies actually arrives on the predicted due date — so treat the date as the centre of a window, not a deadline.
The classic method, named after the German obstetrician Franz Naegele, simply adds 280 days to the first day of your last period. A common shortcut is to take that date, subtract three months and add seven days. Because ovulation happens later in a longer cycle, this calculator adds the difference between your cycle length and 28 days, so women with 32-day cycles get a date roughly four days later than the textbook estimate. If you start from a known conception date instead, the tool counts 266 days forward (38 weeks), since conception occurs about two weeks after the period begins.
| Week | Trimester | What's happening |
|---|---|---|
| 4–6 | First | Missed period, positive test, heartbeat begins forming |
| 8–10 | First | Major organs developing; first prenatal visit usually scheduled |
| 12 | First | End of first trimester; miscarriage risk drops sharply |
| 18–22 | Second | Anatomy ultrasound; you may feel first movements |
| 24 | Second | Viability milestone; glucose screening around now |
| 28 | Third | Third trimester begins; more frequent check-ups |
| 37 | Third | Baby considered full term |
| 40 | Third | Estimated due date |
| 42 | Third | Post-term; induction often discussed |
The date from your last period is an estimate, and it's common for it to shift once you have a scan. An early dating ultrasound between 8 and 14 weeks measures the baby's length and is considered the most accurate way to set the due date — if it differs from the LMP estimate by more than about five to seven days, doctors usually go with the scan. Irregular cycles, uncertainty about the period date, and conception happening earlier or later than expected can all move the figure. That's why this calculator is a starting point: your care team's dated scan takes precedence.
Use the first day of bleeding, not the last day, for the LMP method — this is the single most common error and shifts the date by several days. Adjust the cycle length if yours isn't 28 days; ignoring it can put the estimate off by a week. Don't treat the date as fixed — only around 5% of babies are born on it, and full term spans five weeks. If you used IVF or know your ovulation day, the conception-date method is more accurate than counting from a period you may not remember precisely. And always confirm with a professional; this tool is for general information, not medical advice.
Pregnancy is divided into three trimesters. The first trimester (weeks 1–12) is when the embryo forms its major organs; it often brings the strongest symptoms such as nausea and fatigue. The second trimester (weeks 13–27) is frequently the most comfortable stretch — energy returns, the bump shows, and many people feel the first kicks around week 18 to 22. The third trimester (weeks 28–40+) is about growth and preparation, with more frequent appointments and the body getting ready for labour. Knowing your week tells you which stage you're in and what to expect next, which is exactly what the result above gives you.
It gives a reliable estimate, but only about 5% of babies are born exactly on the predicted date. Most arrive within two weeks either side. An early dating ultrasound is the most accurate way to confirm or adjust the date.
Counting from the first day of your last menstrual period gives a consistent, easy-to-identify starting point. It adds roughly two weeks before conception actually happens, which is why a 40-week pregnancy really involves about 38 weeks of fetal development.
Enter your average cycle length so the tool can adjust for later or earlier ovulation. If your cycles vary a lot, the conception-date method or an early ultrasound will give a more accurate result than the period date alone.
Yes. Switch the method to "conception date" and the tool counts 266 days (38 weeks) forward. This is useful if you tracked ovulation or conceived through IVF and know the exact day.
A pregnancy is considered full term from 37 weeks. Anything from 37 to 42 weeks is normal. Before 37 weeks is preterm, and after 42 weeks is post-term, when induction is often discussed.
No. It is for general information and planning only. Always confirm your due date and any concerns with your midwife, obstetrician or doctor, whose dated scan takes precedence over any estimate.