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Pregnancy Due Date Calculator – When Is My Baby Due?

Estimate your baby’s due date from the first day of your last period, the date of conception or an IVF embryo transfer. See how many weeks pregnant you are today, which trimester you’re in and the dates of key milestones.

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How to use the due date calculator

  1. Choose what you know: your last menstrual period (LMP), the conception date, or an IVF transfer date for a day-3 or day-5 embryo.
  2. Enter the date.
  3. If you use your last period, enter your average cycle length (28 days if you are not sure).

You’ll see your estimated due date, how many days to go, how many weeks and days pregnant you are today, your trimester and a table of milestone dates.

How the due date is worked out

Due date = First day of last period + 280 days + (cycle length − 28)
Due date = Conception date + 266 days
IVF due date = Transfer date + 263 days (day-3 embryo) or + 261 days (day-5 embryo)

Pregnancy is counted from the first day of your last period, about two weeks before conception, so “40 weeks pregnant” is about 38 weeks after conception.

Worked example

Your last period started on 1 January 2026 and your cycles are 28 days:

  • Due date = 1 January 2026 + 280 days = 8 October 2026
  • Conception was probably around 15 January 2026
  • First trimester ends around 8 April 2026
  • Third trimester starts on 16 July 2026 (28 weeks)

With a 32-day cycle, ovulation happens about four days later, so the due date moves to 12 October 2026.

Pregnancy milestones

  • Weeks 4–6 — a home pregnancy test usually turns positive; book your first appointment.
  • Weeks 8–14 — dating scan in many countries; this may adjust your due date.
  • Weeks 18–21 — the anatomy or anomaly scan.
  • Week 24 — the baby is considered viable in many hospitals.
  • Week 28 — the third trimester begins.
  • Week 37 onwards — the baby is early term; full term from 39 weeks.

The calculator lists the dates for these milestones based on your due date. Your own care plan may differ — follow your midwife’s or doctor’s schedule.

If your periods are irregular

When cycles vary a lot from month to month, the date of your last period is a less reliable guide. Your healthcare provider will usually use an early ultrasound measurement instead. You can still use this calculator with your average cycle length for a first estimate.

Privacy

The date you enter stays in your browser — it is never sent to a server or stored anywhere. When you are trying to conceive, the ovulation calculator shows your fertile days. For other date questions, try the age calculator. This calculator gives general information only and is not medical advice; please talk to your midwife, doctor or obstetrician about your pregnancy — see our disclaimer.

Frequently asked questions

How is the due date calculated?

Most doctors and midwives use Naegele’s rule: add 280 days (40 weeks) to the first day of your last menstrual period. If your cycle is longer or shorter than 28 days, the date moves by the difference — for a 32-day cycle, four days later.

If my last period started on 1 January 2026, when is my due date?

With a 28-day cycle, 8 October 2026. With a 32-day cycle, 12 October 2026.

How do I calculate a due date from conception?

Add 266 days (38 weeks) to the conception date. Pregnancy is still counted in weeks from the last period, so on the day of conception you are about 2 weeks pregnant.

How is an IVF due date calculated?

From the transfer date: add 263 days for a day-3 embryo or 261 days for a day-5 blastocyst. IVF due dates are usually the most precise because the embryo’s age is known exactly.

How accurate is the due date?

It is an estimate. Only about 1 in 25 babies is born on the due date itself; most arrive within two weeks either side. An early ultrasound scan, usually between 8 and 14 weeks, can give a more accurate date.

What are the 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. Full term is from 39 weeks.

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