Calculate My Due Date: Pregnancy Due Date Methods

Searching calculate my due date means you want an estimated pregnancy due date. The most common method starts with the first day of the last menstrual period, often called LMP.

Use our Pregnancy Calculator for a quick estimate.

Common Due Date Formula

Estimated due date = First day of LMP + 280 days

This equals 40 weeks of pregnancy counting from LMP.

Example

If the first day of your last period was January 1, adding 280 days gives an estimated due date around October 8 in a non-leap year.

Other Due Date Methods

Your due date may also be estimated from:

• Conception date
• Ovulation date
• IVF transfer date
• Early ultrasound
• Clinical exam and medical history

If your cycles are much shorter or longer than 28 days, LMP dating may be less precise.

Due Date Is an Estimate

A due date is not a deadline. Many pregnancies deliver before or after the estimated date. Healthcare providers may adjust the date if ultrasound measurements suggest a different timeline.

Common Mistakes

Using the last day of the period instead of the first day can shift the estimate.

Assuming conception happened on the LMP date is incorrect. Pregnancy dating convention starts before conception.

Treating the due date as exact can create unnecessary stress.

The Bottom Line

To calculate a due date, add 280 days to the first day of the last menstrual period, then confirm with healthcare guidance.

Use the Pregnancy Calculator for an estimate.

Medical note: This article is informational only and is not medical advice. For pregnancy dating and prenatal care, consult a qualified healthcare professional.

How to Calculate: Step-by-Step Guide

1

Start with LMP

Use the first day of your last menstrual period when known.

2

Add 280 days

A common estimate adds 40 weeks, or 280 days, to the LMP date.

3

Adjust with clinical guidance

Ultrasound dating, cycle length, or IVF details may change the estimate.