Pregnancy Calculator

How to Estimate Your Due Date Wondering when you’ll meet your baby? A pregnancy calculator is the quick, easy tool every expectant parent uses first. But how does it work, and can you figure it out yourself with just a calendar? The answer is yes. Let’s break down the simple math behind your due date. 

The Magic Number: 280 Days Despite how it feels, pregnancy isn’t exactly 9 months long in medical terms. It’s typically **40 weeks** from the first day of your last menstrual period (LMP). This adds up to about 280 days. Why count from your period, and not conception? It’s simple: most people can pinpoint the start of their last period, but it’s much harder to know the exact day of ovulation or conception. This standard gives doctors and midwives a consistent starting point. 

How to Manually Calculate Your Due Date You can be your own pregnancy calculator with just three steps. Grab a calendar and follow along: 

1. Find the Date: Mark the first day of your last menstrual period

2. Use the Rule: Apply Naegele’s Rule: Add 1 year, subtract 3 months, and add 7 days. 

3. Do the Math: Let’s use an example. If your LMP was June 10, 2024: Add 1 year: June 10, 2025. Subtract 3 months: March 10, 2025.