Due Date Calculator
Estimate your baby's due date from your last menstrual period and cycle length.
The Due Date Calculator estimates your expected delivery date based on Naegele's rule. Enter the day of your last menstrual period (as day number from January 1st) and your average cycle length.
The standard calculation adds 280 days (40 weeks) to your LMP date, with an adjustment for cycle lengths other than the standard 28 days. A longer cycle shifts the due date later; a shorter cycle shifts it earlier.
Keep in mind that only about 5% of babies are born on their exact due date. Most are born within two weeks before or after. Your healthcare provider may adjust the date based on ultrasound measurements.
Frequently Asked Questions
How is the due date calculated?
Using Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period, adjusted for cycle length variations from 28 days.
How accurate is the due date?
Only about 5% of babies arrive on the estimated due date. Most deliveries occur between 38-42 weeks. First-time mothers tend to deliver a few days late.
What if my cycle is irregular?
For irregular cycles, an early ultrasound (8-12 weeks) provides a more accurate due date than LMP-based calculation.