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Pregnancy Due Date Calculator

Estimate your due date from the first day of your last period, the date of conception or an IVF embryo transfer, and see how far along you are today with the key dates ahead.

days

From the first day of one period to the first day of the next. 28 days is the usual assumption; enter 21 to 45.

Enter a date to see the estimated due date.

This is an estimate only. Only about 4–5% of babies arrive on their due date, and most are born in the weeks around it. Your doctor or midwife may adjust the date after an ultrasound scan. This calculator is not medical advice.

How to use the due date calculator

  1. Choose what to calculate from: Last period, Conception or IVF transfer.
  2. Enter the date – the first day of your last period, the conception date or the embryo transfer date.
  3. Adjust the details. For Last period, set your average cycle length (21 to 45 days, 28 by default). For IVF transfer, choose Day-3 embryo or Day-5 embryo.
  4. Read the estimated due date, how many weeks and days pregnant you are today, which trimester you are in and the key dates list.

Features

  • Three methods: last menstrual period (Naegele's rule), conception date and IVF transfer for day-3 or day-5 embryos.
  • Cycle length adjustment from 21 to 45 days for the last period method.
  • Weeks and days today, the current trimester and the number of days until the estimated due date.
  • Key dates: end of the first trimester (13 weeks 6 days), the 20-week scan window (18 weeks to 20 weeks 6 days), the start of the third trimester (28 weeks), full term (37 weeks) and the due date (40 weeks). Dates that have passed are greyed out.
  • Clear messages for a date in the future, a cycle length outside 21 to 45 days or a date more than 42 weeks ago.

How each method works

Last period: due date = first day of the last period + 280 days + (cycle length − 28). If your period started on 1 January 2026 and your cycle is 28 days, the estimate is 8 October 2026. With a 35-day cycle it moves to 15 October 2026.

Conception: due date = conception date + 266 days. Conception on 15 January 2026 also gives 8 October 2026, because conception is assumed to happen about 14 days after the start of a 28-day cycle.

IVF transfer: due date = transfer date + 266 days − the embryo's age. A day-5 embryo transferred on 20 January 2026, or a day-3 embryo transferred on 18 January 2026, both give 8 October 2026.

Weeks are counted from 40 weeks before the estimated due date, so the week you see is the same whichever method you use.

Trimesters

The calculator uses a common definition: the first trimester runs up to 13 weeks 6 days, the second from 14 weeks to 27 weeks 6 days, and the third from 28 weeks until birth. Some books and apps draw the lines a week earlier or later, so do not worry if another source differs slightly.

Please keep in mind

This tool does date arithmetic only. It cannot tell you anything about your health or your baby's. Only about 4–5% of babies arrive on the due date itself, and your doctor or midwife may adjust the date after an ultrasound scan. If you have questions about your pregnancy, please speak to a qualified healthcare professional. This page is not medical advice.

Why use Fileora's due date calculator

It gives you the estimate, how far along you are today and the dates worth putting in your calendar, all in one place. It is free, needs no sign-up and works on any phone. Because the calculation happens on your device, no dates are sent anywhere.

To count the days between any two dates, try the date difference calculator. Once the baby has arrived, the age calculator shows an exact age in years, months and days.

Frequently asked questions

How is the due date calculated from my last period?

The calculator uses Naegele's rule: it adds 280 days (40 weeks) to the first day of your last menstrual period. That assumes a 28-day cycle, so if your cycles are longer or shorter the date moves by the difference. With a 32-day cycle, for example, the estimate is 4 days later.

Why are pregnancy weeks counted from my last period and not from conception?

Because most people know when their last period started but not when they conceived. By convention the count starts about two weeks before conception, so at conception you are already counted as roughly 2 weeks pregnant. The calculator uses the same convention for every method.

How accurate is the due date?

It is an estimate. Only about 4–5% of babies are born on their due date, and most arrive in the weeks around it. Your doctor or midwife may change the date after an ultrasound scan, especially if your cycles are irregular. This calculator is not medical advice.

How does the IVF due date work?

With IVF the age of the embryo is known exactly. The calculator adds 263 days to the transfer date for a day-3 embryo and 261 days for a day-5 embryo, which lands on the same point as 266 days from conception. Your clinic may give you its own date, and that is the one to follow.

When is the 20-week scan?

The mid-pregnancy anomaly scan is usually offered between 18 weeks and 20 weeks 6 days, which is the window shown in the key dates. Your own appointment is arranged by your maternity care provider and may fall at a slightly different time.

What does full term mean?

A pregnancy is generally described as full term from 37 weeks. The calculator shows the date you reach 37 weeks alongside the estimated due date at 40 weeks.

Is my information saved?

No. The dates are worked out in your browser and nothing is stored or sent to a server. When you close the page, the information is gone.

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