Gestational Age Calculator

The gestational age calculator estimates the current pregnancy age in weeks and days. It supports three real-world dating methods: last menstrual period, conception date, or ultrasound date with weeks and days at the scan. The result also shows an estimated due date, an estimated conception date, trimester, development milestones, and recommended appointment timing.

How to use this calculator

Choose the method that matches the information you have. For LMP, enter the first day of the last menstrual period. For conception, enter the known or estimated conception date. For ultrasound, enter the scan date plus the reported pregnancy age in weeks and days. Then set calculate as of to today or another date.

For related pregnancy dating, compare results with the pregnancy conception calculator or work backward from a due date with the reverse due date calculator.

How it works

Gestational age is counted from the pregnancy dating start date, not always from fertilization.

$gestational\ days = as\ of\ date - dating\ start\ date$

For conception dating, the calculator estimates the dating start as 14 days before conception. For ultrasound dating, it adds elapsed days since the scan to the scan age.

Worked example

If the LMP was January 1 and the as-of date is March 5, the elapsed time is 63 days, or 9 weeks, 0 days. The estimated due date is 280 days after the LMP.

Interpreting the timeline

Milestones and appointment labels are general timing guides, not medical instructions. Cycle variation, uncertain dates, and later scan differences can change dating. Use clinical guidance for prenatal care decisions.