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Uses the standard 280-day rule, adjusted for cycle length. An estimate, not a diagnosis.
Pregnancy Due Date Calculator
Estimate your due date from the first day of your last period, a known conception date, or an IVF embryo transfer. You also get how far along you are today, your trimester, and the dates of key milestones. Nothing you enter leaves your device.
-Estimated due date
-How far along today
-Trimester
Only about 1 in 25 babies arrives on the exact due date; most arrive within a week or two either side. Your midwife or doctor may adjust the date after an early ultrasound.
How the due date is calculated
Pregnancy is counted from the first day of your last menstrual period (LMP), about two weeks before conception. A typical pregnancy lasts 280 days (40 weeks) from that date. This is Naegele's rule, the same method most clinics use for a first estimate.
- From last period: due date = LMP + 280 days + (cycle length − 28).
- From conception: due date = conception + 266 days.
- IVF, day 3 transfer: due date = transfer + 263 days. Day 5 transfer: transfer + 261 days.
Worked example
Last period started 1 March 2026 with a 28-day cycle. 1 March + 280 days = 6 December 2026. With a 32-day cycle, ovulation is about 4 days later, so the estimate moves to 10 December 2026.
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. Pregnancy is considered full term from 37 weeks, and post-term after 42 weeks.
Limitations
A due date is an estimate. Irregular cycles, uncertain period dates and natural variation all shift it. A dating ultrasound in the first trimester is the most accurate way to confirm it. This calculator is for information only and is not medical advice; always follow the guidance of your midwife or doctor.
Planning estimate only. Results use the list prices shown and may differ from your actual bill. Terms
Frequently asked questions
How is my due date calculated?
By adding 280 days (40 weeks) to the first day of your last period, adjusted if your cycle is longer or shorter than 28 days. From a known conception date, add 266 days instead.
How accurate is a due date calculator?
It gives a good estimate, but only about 4 percent of babies are born on their due date. Most arrive between 37 and 42 weeks. An early ultrasound gives the most accurate date.
Why does pregnancy count from my last period and not conception?
Because the date of the last period is usually known while conception is not. By convention, week 1 of pregnancy starts on the first day of the last period, about two weeks before you actually conceive.
How do I calculate my due date after IVF?
Use the transfer date. For a day 5 blastocyst, add 261 days; for a day 3 embryo, add 263 days. Choose the matching IVF option in the calculator.
How many weeks pregnant am I?
Choose your method and enter the date. The calculator shows how far along you are today in weeks and days, counted from the LMP-equivalent start date.