Find your due date and how far along you are

Enter the first day of your last period and your usual cycle length to see your estimated due date, how many weeks pregnant you are today, and the key dates ahead.

First day of last period

The day your last period started.

Cycle length (days)

Usually 28; from 21 to 45.

Calculations run on this device. We don't see, store or log the numbers you enter.

Not reviewed by a clinician. For health decisions, talk to a doctor.

How it works

Enter the first day of your last menstrual period.
Enter your usual cycle length in days (28 if you're not sure).
Read your due date, today's week and trimester, and the dates when each trimester starts.

How the due date is worked out

Doctors date a pregnancy from the first day of the last period, not from conception. The due date is that day plus 280 days (40 weeks), a rule known as Naegele's rule. For cycles longer or shorter than 28 days, every date moves by the difference: with a 35-day cycle, a period starting on 15 March 2026 gives a due date of 27 December instead of 20 December. Counting exactly 280 days can differ by a day or two from the older "add 9 months and 7 days" shortcut.

Weeks and 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. A pregnancy is full term from 37 weeks. Only about 1 in 20 babies arrives on the due date itself; most arrive within two weeks either side of it.

Your scan date comes first

If you have had an early ultrasound scan, the due date from the scan is more accurate than one from your period and is the one your doctor or midwife will use. This calculator is for planning and curiosity, not for medical decisions.

Worked examples

Due dates from the last period (280 days, adjusted for cycle length)
Last period	Cycle (days)	Due date	Estimated conception
January 1, 2026	28	October 8, 2026	January 15, 2026
March 15, 2026	28	December 20, 2026	March 29, 2026
March 15, 2026	35	December 27, 2026	April 5, 2026
June 10, 2026	24	March 13, 2027	June 20, 2026

Frequently asked questions

How many weeks pregnant am I?

The calculator shows it from today's date on your device, counted from your last period adjusted for your cycle length, in weeks and days.

I don't know my cycle length. What should I enter?

Leave it at 28 days, the usual value. If your cycles are irregular, your due date from an early scan will be much more reliable.

When did I conceive?

The estimate is about 2 weeks after the adjusted period date, which is when ovulation usually happens. The real date can differ by several days.