Pregnancy Calculator

This pregnancy calculator estimates your expected due date and key pregnancy milestones using the date of your last menstrual period (LMP) and your average cycle length. The most commonly used method, Naegele's Rule, adds 280 days (40 weeks) to the first day of the last menstrual period to estimate the estimated date of delivery (EDD). The tool is designed to provide quick, accessible timeline estimates you can use for planning and prenatal awareness.

It's important to understand that the gestational age calculated from LMP counts from the first day of the last period, not from conception. Conception usually occurs about two weeks after the first day of the LMP in a typical 28-day cycle, so gestational age will typically be about two weeks greater than fetal age (time since conception).

How to interpret the results

The calculator provides an EDD and outlines trimester boundaries and milestone weeks. Most births occur within a two-week window either side of the estimated date, and only a small percentage of births occur exactly on the predicted day. If you have irregular cycles or are unsure of your LMP, an early ultrasound (first trimester) is often more reliable for accurate dating.

When to get medical dating

For precise dating, clinicians use ultrasound measurements of the embryo or fetus in early pregnancy. Ultrasound also helps confirm viability, detect multiples, and screen for certain conditions. Discuss any dating concerns with your healthcare provider so they can schedule appropriate ultrasound assessments and prenatal care.

Limitations and privacy

This calculator is an informational tool only. It runs in your browser and does not transmit personal data to our servers. Use the results to plan appointments and track milestones, but rely on healthcare professionals for medical advice and decisions.