Due Date Calculator
Estimate your pregnancy due date from your last period, conception date or IVF transfer, with gestational age, trimester and milestone dates.
Pick a date above — the due date is worked out as you type.
- Estimated due date
- —
- Gestational age
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- Trimester
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- Estimated conception
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- Days remaining
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0% of 40 weeks
| Milestone | Date | Gestational age |
|---|---|---|
| Pregnancy dating starts | — | 0w 0d |
| Second trimester begins | — | 14w 0d |
| Viability milestone | — | 24w 0d |
| Third trimester begins | — | 28w 0d |
| Full term begins | — | 37w 0d |
| Estimated due date | — | 40w 0d |
| Post-term | — | 42w 0d |
These dates are estimates, not medical advice. Only about 4% of babies arrive on the estimated due date, and a dating ultrasound is more accurate than any calendar method. Always confirm your dates with a midwife or doctor.
How it works
The classic due-date formula is Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period. That assumes a textbook 28-day cycle with ovulation on day 14, so this calculator also lets you enter your own average cycle length and shifts the due date by the difference — a 32-day cycle pushes it four days later, a 26-day cycle pulls it two days earlier. If you know the conception or ovulation date instead, it adds 266 days; for IVF it counts 261 days from a day-5 blastocyst transfer and 263 days from a day-3 embryo transfer.
From that due date it works backwards to show how far along you are today (or on any date you pick), which trimester that falls in, the estimated conception date and the dates of the milestones that matter: the start of the second and third trimesters, the 24-week viability mark, full term at 37 weeks and post-term at 42 weeks. Every calculation runs in plain JavaScript in your browser using UTC date maths, so nothing about your pregnancy is uploaded, stored or tracked — and there are no ads or sign-ups.
Frequently asked questions
How is a due date calculated?
The standard method is Naegele's rule: add 280 days — 40 weeks — to the first day of your last menstrual period. That works because pregnancy is dated from the last period rather than from conception, which adds roughly two weeks you were not actually pregnant for. If you know the conception or ovulation date instead, the due date is 266 days later. For IVF the dating is exact: 261 days from a day-5 blastocyst transfer and 263 days from a day-3 embryo transfer. This calculator supports all four methods and shows the resulting date instantly.
How accurate is a due date calculator?
It gives an estimate, not a delivery date. Only about 4% of babies are born on their estimated due date, and roughly 80% arrive in the two weeks either side of it, so treat it as the centre of a window rather than an appointment. A first-trimester dating ultrasound is more accurate than any calendar method because it measures the baby directly, and your midwife or doctor may move your due date if the scan disagrees with your last period by more than about a week. These results are estimates only and are not medical advice.
How do I calculate my due date if my cycle is not 28 days?
Naegele's rule assumes a 28-day cycle with ovulation on day 14, so a longer or shorter cycle shifts everything. Add the difference between your average cycle length and 28 days to the due date: a 32-day cycle means you ovulate about four days later, so the due date moves four days later; a 26-day cycle moves it two days earlier. Enter your own average cycle length in the field on this page and the due date, gestational age and every milestone date are recalculated for you.