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Pregnancy Due Date Calculator

Estimate your baby's due date from the first day of your last period, and see how far along you are.

Usually 28 days. Count from the first day of one period to the first day of the next.

Estimated due date

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How far along you are
Trimester
Estimated conception
Second trimester starts
Third trimester starts
Days until due date

How to use the due date calculator

Enter the first day of your last menstrual period and your usual cycle length. The calculator estimates your due date, shows how many weeks and days pregnant you are today, and lists the key dates of each trimester.

Naegele's rule

Due date = first day of last period + 280 days + (cycle length − 28)

For example, if your last period started on January 1 and your cycle is 28 days, your estimated due date is October 8. With a 32-day cycle it moves 4 days later, to October 12.

Pregnancy milestones

  • Weeks 1–13 (first trimester): the baby's organs form; many people have their first ultrasound.
  • Weeks 14–27 (second trimester): often the most comfortable stretch; the anatomy scan happens around week 20.
  • Weeks 28–40 (third trimester): the baby gains most of its weight. A pregnancy is considered full term from week 39.

This calculator gives an estimate for information only. Your doctor or midwife will confirm your due date, usually with an ultrasound.

Frequently asked questions

How is the due date calculated?

The standard method, Naegele's rule, adds 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 is shifted by the difference, because ovulation happens later or earlier.

How accurate is a due date?

Only about 4% of babies arrive on their exact due date. Most are born within two weeks either side. An early ultrasound, ideally in the first trimester, gives the most accurate estimate.

Why is pregnancy counted from my last period?

The exact day of conception is rarely known, but the first day of the last period usually is. So pregnancy is dated from that day, about two weeks before conception. That's why you're considered “2 weeks pregnant” at conception.

When does each trimester start?

The first trimester runs from week 1 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.

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