Pregnancy Due Date Calculator — Free Online Tool

The Pregnancy Due Date Calculator estimates a due date from the first day of your last menstrual period, using Naegele's rule — 280 days, or 40 weeks.

The detail that confuses nearly everyone is that pregnancy is dated from the last period rather than from conception, which occurs roughly two weeks later. So at the point someone is described as "four weeks pregnant", conception was about two weeks earlier. This convention exists because the date of a period is something people usually know, while the date of conception generally is not.

A due date is a midpoint, not a deadline, and the spread around it is wide. Only a small percentage of babies arrive on the estimated date, and full term covers 37 to 42 weeks. Treating the date as an appointment produces a lot of unnecessary anxiety in the days after it passes.

Accuracy also depends on the assumption of a 28-day cycle with ovulation on day 14. For someone with consistently longer or shorter cycles, the estimate shifts accordingly. This is why an early ultrasound — particularly in the first trimester, when fetal size varies least between pregnancies — gives a more accurate date than the calculation and will normally supersede it in your medical records.

This is general information and not a substitute for prenatal care. Your midwife or doctor's dating, based on scans and clinical assessment, is the one to rely on.

Calculation happens entirely in your browser; nothing you enter is transmitted or stored.

Our Pregnancy Due Date Calculator is completely free to use with no signup required. For this tool, processing runs in your browser — your files and data stay on your device and are not uploaded to our servers.

Whether you are a developer, designer, student, or business owner, this tool is designed to save you time and make your workflow more efficient. Bookmark this page to access it whenever you need it — it will always be free.