Pregnancy Due Date Calculator

Enter the first day of your last period and your usual cycle length and this estimates a due date, tells you how many weeks along you'd be today, and shows when each trimester ends. It's for general planning. Your midwife or doctor will confirm your dates, often with an ultrasound.

How to use it

1. Enter the first day of your last period.
2. Enter your usual cycle length.
3. Read the estimated due date.
4. Check the trimester dates.

When it helps

• Planning for a baby's arrival.
• Understanding how many weeks along you are.
• Preparing questions for appointments.
• Sharing an approximate date with family.

Good to know

• Only about 5 percent of babies are born on the due date.
• A scan may adjust the date your provider gives you.
• If your cycles are irregular, the estimate is less reliable.

How the date is estimated

The standard method, called Naegele's rule, adds 280 days, or 40 weeks, to the first day of the last period. This assumes a 28-day cycle with ovulation on day 14. If your cycle is longer or shorter, the tool shifts the date by the difference.

Pregnancy is counted from the last period, not from conception, so when you're "4 weeks pregnant" conception happened only about two weeks earlier.

Worked example

If the last period began on 1 July 2026 and the cycle is 28 days, the due date comes out as 7 April 2027. The tool also shows when each trimester ends: the first at the end of week 13, the second at the end of week 27.

A normal pregnancy runs from 37 to 42 weeks, so the real birth could fall several weeks either side of the estimate.

What to do with the estimate

Book your first appointment early, and take the date to your midwife or doctor. They may offer an ultrasound, usually around 8 to 14 weeks, which can refine the date.

This page is for planning, not medical advice. If you have concerns about your pregnancy, contact a healthcare professional rather than relying on a calculator.

Understanding pregnancy weeks

Pregnancy is divided into three trimesters: weeks 1 to 13, 14 to 27, and 28 to the birth. A baby is considered early term at 37 to 38 weeks, full term at 39 to 40, and late term at 41. Births before 37 weeks are premature.

Your care team will talk about gestational age, which is the number of weeks since the last period, and may adjust it after a scan.

Keeping track

Write the estimated date and the date of your last period together in your notes, so you can show them at your first appointment. Any change after a scan can then be recorded next to the original.

Questions