Weeks to Months Pregnant

About this calculator

Obstetricians track pregnancy in completed weeks from the first day of your last menstrual period, since it is the most precise and consistent unit for scheduling scans, tests and due-date calculations — but most people naturally think in months. There is no single official conversion because months are not a fixed number of weeks, so the widely used approximation is 4.3 weeks per month (40 weeks divided across roughly 9 months), rather than the simpler but less accurate 4-weeks-per-month lunar-month shortcut.

Knowing your month count still matters for everyday milestones — moving from the first to second trimester around month 3, entering the “third trimester” conversation around month 7, or simply answering the question every pregnant person gets asked constantly. The rough mapping also helps compare notes with older due-date charts, baby-size comparisons and pregnancy apps that mix weeks and months interchangeably.

This calculator takes your current pregnancy week and converts it into the equivalent number of months using the standard obstetric approximation.