Pregnancy Due Date Calculator
Enter the first day of your last period to estimate your baby's due date, using the standard 40-week (Naegele's rule) method.
How this is calculated
This calculator applies Naegele's rule, the standard formula obstetricians use for a first-pass due date: it adds 280 days (40 weeks) to the first day of your last menstrual period. Your current gestational age is the number of full weeks and days that have passed since that date, and the countdown shows how many days remain until the estimated due date — or how many days past it you are, if it's already gone by. This is an estimate based on a typical 28-day cycle; your own cycle length, ovulation timing, or a doctor's ultrasound measurement can shift the real date earlier or later.
Frequently asked questions
How is a due date calculated?
This calculator uses Naegele's rule: it adds 280 days (40 weeks) to the first day of your last menstrual period. It's a widely used estimate, not a prediction — only about 5% of babies are actually born on their exact due date, and most arrive within about two weeks of it.
Is this the same as an ultrasound due date?
Not necessarily. This tool uses the standard last-menstrual-period (LMP) method. A doctor's ultrasound-based estimate, especially from an early first-trimester scan, is generally considered more accurate for an individual pregnancy and should take precedence if the two dates differ.
Is this medical advice?
No. This is a simple date calculator based on a standard obstetric formula, not medical advice or a diagnosis. Always confirm dates and discuss your pregnancy with a qualified healthcare provider.