Pregnancy Due Date Calculator

Enter your LMP to calculate your due date.

For informational purposes only. Always confirm with your healthcare provider.

What is a Due Date Calculator?

A pregnancy due date calculator estimates the date your baby is expected to arrive based on the first day of your last menstrual period (LMP). It also shows your current week of pregnancy, which trimester you are in, and how many days remain until your due date.

How It Works

This calculator uses Naegele's Rule, the standard clinical method:

Due date = LMP + 280 days (40 weeks)
Week of pregnancy = days since LMP / 7
Trimester 1  : weeks 1-13
Trimester 2  : weeks 14-27
Trimester 3  : weeks 28-40

Example

LMP was August 1:

  • Due date: August 1 + 280 days = May 8 (next year)
  • At 10 weeks: still in the first trimester
  • At 20 weeks: mid-second trimester, around December

Tips

  • Only about 4% of babies are born on their exact due date. The normal delivery window is 37 to 42 weeks.
  • If you had an early ultrasound, your provider may adjust the due date based on the baby's measurements rather than your LMP.
  • The LMP method assumes a 28-day cycle with ovulation on day 14. If your cycle is shorter or longer, your actual due date may differ slightly.

Frequently Asked Questions

What is the LMP method?

LMP stands for Last Menstrual Period. Since the exact date of conception is rarely known, doctors date a pregnancy from the first day of the last period instead. This is why pregnancy is counted as 40 weeks even though fertilization typically happens around week 2.

How accurate is the estimated due date?

The LMP method is accurate to within 1-2 weeks for most pregnancies. An ultrasound in the first trimester can refine this estimate by measuring the fetus directly, which is more precise when cycle length varies.

What are the three trimesters?

The first trimester covers weeks 1 through 13, the second trimester weeks 14 through 27, and the third trimester weeks 28 through 40. Most major organ development occurs in the first trimester, while growth and maturation continue through the third.

When is a baby considered full term?

Full term is 39 to 40 weeks. Babies born at 37-38 weeks are early term, and those born at 41+ weeks are late term. The healthiest outcomes are generally associated with deliveries between 39 and 40 weeks.