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Pregnancy Calculator

Find out how many weeks pregnant you are today, which trimester you are in, how many days are left until your due date and when the key pregnancy milestones fall.

Calculate based on
21 to 45 days. Use 28 if you are not sure.

This is an estimate based on today's date on your device, not medical advice. An ultrasound scan gives a more reliable date. Follow the advice of your doctor or midwife.

How to use the pregnancy calculator

Pick the date you know best:

  • Last period: the first day of your last menstrual period, plus your average cycle length (21 to 45 days; use 28 if you are not sure).
  • Conception date: the day you conceived, if you know it.
  • Due date: the due date you were given, for example after an ultrasound scan.

Press Calculate. The result answers the question "how many weeks pregnant am I?" in weeks and days, and also shows your trimester, your due date, the number of days to go and how much of a 40-week pregnancy is complete. The milestone table lists the dates for the end of the first trimester, approximate viability, the start of term, the due date and 42 weeks, and marks which ones have already passed. Today's date is taken from your device.

How weeks of pregnancy are counted

Pregnancy weeks are counted from the first day of the last period, about two weeks before conception. That is why you are already said to be "4 weeks pregnant" around the time a period is missed.

  • From your last period, the start date moves by one day for each day your cycle is longer or shorter than 28 days.
  • From a conception date, the start date is 14 days earlier.
  • From a due date, the start date is 280 days (40 weeks) earlier.

The number of days since the start date, divided by 7, gives the completed weeks; the remainder gives the extra days. The first trimester lasts until 13 weeks 6 days, the second until 27 weeks 6 days, and the third until birth.

Worked example

If your last period started on February 2, 2026, your cycle is 28 days long and today is June 15, 2026, then 133 days have passed. That is 19 weeks and 0 days, in the second trimester. The due date is Monday, November 9, 2026, with 147 days to go, and the pregnancy is 47.5% complete. The first trimester ended on May 10, approximate viability is reached on July 20 and term begins on October 19.

Good to know

  • Babies born from 37 weeks are considered term. Doctors further split this into early term (37–38 weeks), full term (39–40 weeks) and late term (41 weeks).
  • "Viability" around 24 weeks is a rough medical reference point, not a guarantee; outcomes depend on many factors and on the care available.
  • A dating scan in early pregnancy is more accurate than any calculator. If your scan gives a different due date, enter it with the due date method.
  • This calculator gives estimates, not medical advice. Always follow the guidance of your doctor or midwife.

Frequently asked questions

How many weeks pregnant am I?

Count the days from the first day of your last period to today and divide by 7: the whole number is your completed weeks and the remainder is the extra days. The calculator does this for you and adjusts for cycles longer or shorter than 28 days.

Why am I counted as pregnant before I conceived?

By convention, pregnancy is dated from the first day of the last period because that date is usually known, while the exact day of conception is not. Conception typically happens about two weeks later, so the first two weeks of a pregnancy count are before conception.

Which trimester am I in?

The first trimester runs from the start of pregnancy to 13 weeks 6 days, the second from 14 weeks 0 days to 27 weeks 6 days, and the third from 28 weeks 0 days until birth. The calculator shows your current trimester based on today's date.

What does the percent complete mean?

It shows how many days of a standard 280-day (40-week) pregnancy have passed. For example, at 20 weeks you are 50% of the way to your due date. After the due date the value stays at 100%.

Can I rely on these dates?

They are estimates only and are not medical advice. Your doctor or midwife will confirm your dates, usually with an ultrasound scan, and that date should guide your care.