Due Date Calculator

What is due date calculator?

A pregnancy due date calculator estimates your baby's expected arrival date using Naegele's rule — the standard method taught in obstetrics. Enter the number of days since the first day of your last menstrual period (LMP), and optionally your average cycle length if it differs from the standard 28 days. The calculator then estimates how many days remain until the due date (based on a 280-day pregnancy adjusted for cycle length), your current pregnancy week, and which trimester you are in. Only about 5% of babies are born on their exact due date; a full-term window of 37–42 weeks is normal. This tool is intended for informational use — your doctor or midwife will refine the estimate using ultrasound measurements, especially in the first trimester. All calculations are private and run entirely in your browser.

How to use this calculator

1. Enter your days since last period started.
2. Enter your average cycle length.
3. Click the "Calculate" button.
4. View your result instantly — the main result is displayed prominently at the top with a detailed breakdown below it.

When to use this calculator

• Estimating a due date from the first day of the last menstrual period
• Tracking which pregnancy week and trimester you are currently in
• Adjusting the estimate for longer or shorter menstrual cycles
• Planning prenatal appointments and milestones around the due date
• Understanding how the 40-week pregnancy timeline maps to calendar dates