Pregnancy Due Date Calculator
Enter the first day of your last menstrual period to get an estimated due date.
Frequently asked questions
How is my due date calculated?
This tool uses Naegele's Rule: it takes the first day of your last menstrual period, adds 280 days (40 weeks), and adjusts for a cycle length other than the 28-day average. It's an estimate — most babies arrive within two weeks of this date, not on it exactly.
Why does my cycle length matter?
A longer or shorter cycle shifts when you likely ovulated, which shifts your estimated conception date and therefore your due date.
Is this accurate for everyone?
LMP-based estimates are less precise for irregular cycles. An early ultrasound generally gives a more accurate estimate than LMP alone — bring your LMP date to your first consultation and your doctor can confirm or adjust it.
Does this tool store my information?
No. The calculation happens entirely in your browser and nothing you enter here is saved or sent anywhere.