👶Pregnancy Due Date Calculator

Estimate your due date based on your last menstrual period.

First Day of Last Menstrual Period

Based on Naegele's rule: LMP + 280 days (40 weeks)

About Pregnancy Due Date Calculator

This pregnancy due date calculator uses Naegele's rule to estimate your expected delivery date by adding 280 days (40 weeks) to the first day of your last menstrual period. It also shows your current gestational age in weeks and days, and outlines important pregnancy milestones by trimester. While every pregnancy is unique, this estimate gives you a reliable planning target.

How to Use Pregnancy Due Date Calculator

1
Enter your LMP date
Input the first day of your last menstrual period into the calculator.
2
View your due date
The tool calculates your estimated due date 40 weeks from your LMP.
3
Check your milestones
Review your current gestational age and key trimester milestones on the results page.

Common Use Cases

Getting an initial due date estimate before your first OB appointment
Calculating how far along you are in your pregnancy
Planning maternity leave around an expected delivery window
Tracking trimester progression and upcoming prenatal milestones

Frequently Asked Questions

How accurate is the due date calculation?

Only about 5% of babies are born on their exact due date. The calculation gives a 40-week estimate from your last menstrual period, but full-term deliveries typically occur anywhere from 38 to 42 weeks. Your OB or midwife may adjust the date after an early ultrasound.

What if I don't know my last menstrual period date?

If you're unsure of your LMP, an ultrasound in the first trimester (ideally between 8–12 weeks) can measure the embryo and provide a highly accurate gestational age and due date estimate.

What does gestational age mean?

Gestational age is the number of weeks since the first day of your last menstrual period — not from the date of conception. At the time of a missed period, most people are already considered 4 weeks pregnant by this measure.