Pregnancy Calculator

Purpose: Track how far along you are - current pregnancy week, trimester, days remaining and estimated due date - from your LMP.

First day of last period (LMP)

Pregnancy Calculator

The Pregnancy Calculator tracks your pregnancy week by week from your last menstrual period, showing your current week, trimester, and estimated due date.

How pregnancy dating works

Pregnancy is conventionally dated from the first day of your last menstrual period (LMP), not conception, and lasts about 40 weeks. From your LMP the calculator works out how many weeks and days along you are, which trimester you are in, and your estimated due date (LMP + 280 days).

Trimesters at a glance

First trimester - weeks 1–12.
Second trimester - weeks 13–27.
Third trimester - week 28 to birth.

This is an estimate for guidance and excitement, not a medical assessment. Only about 4% of babies arrive on the exact due date, and your doctor's ultrasound dating takes precedence.

Frequently Asked Questions

Why is pregnancy dated from the last period, not conception?

Because the LMP date is easy to know precisely, while the exact conception date usually is not. Standard dating adds about two weeks before conception.

How is the due date calculated?

It is estimated as 280 days (40 weeks) from the first day of your last menstrual period, known as Naegele's rule.

Which trimester am I in?

Weeks 1-12 are the first trimester, 13-27 the second, and 28 onward the third. The calculator shows your current week and trimester.

Will my baby arrive on the due date?

Rarely exactly. Only around 4% of births happen on the estimated due date; most occur in the surrounding two weeks.