What is a Pregnancy Due Date Calculator?

A Pregnancy Due Date Calculator is a medical forecasting tool used by obstetricians and expectant parents to estimate the Expected Date of Delivery (EDD). Since only about 4-5% of babies are born exactly on their due date, this date serves as an essential anchor point for tracking fetal development and scheduling medical checkups.

How Does the Due Date Calculator Work?

Our calculator primarily relies on Naegele's Rule, which is the standard medical formula used worldwide. By inputting the First Day of your Last Menstrual Period (LMP) and your average cycle length, the engine calculates the exact date you will hit the 40-week gestation mark.

The Naegele's Rule Mathematical Formula

Naegele's Rule assumes a standard 28-day menstrual cycle, with ovulation occurring on day 14. The formula is:

EDD = LMP Date + 7 days - 3 months + 1 year

(Or simply: LMP + 280 days)

If your average cycle is longer or shorter than 28 days, our calculator automatically adjusts the 280-day baseline to account for the delayed or early ovulation, giving you a mathematically personalized result.

Major Benefits of Calculating Your Due Date

Medical Tracking: Allows your doctor to accurately measure fetal growth against standard percentile charts for a specific gestational age.
Maternity Leave Planning: Gives you a hard date to provide HR when organizing financial and professional arrangements.
Trimester Milestones: Knowing your exact weeks and days pregnant helps you understand the physiological changes happening to your body week-to-week.