Pregnancy Due Date Calculator
Estimate your due date and current gestational week instantly — nothing is uploaded.
How the due date is calculated
This calculator uses Naegele's rule, the standard obstetric formula: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). The LMP is used rather than the estimated conception date because it is the date most reliably known at the start of prenatal care. Your gestational age is the number of weeks and days elapsed since the LMP.
The reference date field defaults to today so you can read your current gestational week immediately. You can change it to any date to see what gestational age you will be on a future appointment. Everything is calculated locally — nothing is sent to a server.
FAQ
What is the LMP date? The first day of bleeding of your most recent menstrual period, not the last day. This is the standard clinical starting point.
Is 40 weeks the same as 9 months? Pregnancy is counted in weeks, not calendar months. 40 weeks is roughly 9 calendar months, but the week count is always the precise clinical measure.
My scan shows a different gestational age — which is right? Ultrasound dating may differ by days. Your healthcare provider will decide which date to use.
Not medical advice. This tool provides estimates only. Always consult a qualified healthcare provider for clinical decisions.