Health
Pregnancy Due Date Calculator
Calculate your estimated due date, gestational age, and trimester progress using Naegele's rule.
Inputs
Results
Estimated Due Date
Select LMP Date
Gestational Age
0 Weeks, 0 Days
Trimester
-
Days Until Delivery
0 Days
How It Works
The pregnancy calculator estimates delivery dates using Naegele's rule, a clinical standard. The method takes the first day of your last menstrual period (LMP), adds 280 days (40 weeks), and adjusts for average menstrual cycles that differ from the standard 28-day cycle.\n\nWeeks of gestation are calculated by counting the elapsed time from the LMP date. This gestational age dictates the trimester splits: Trimester 1 (0 to 12 weeks), Trimester 2 (13 to 26 weeks), and Trimester 3 (27 weeks to delivery).
Formula Used
Estimated Due Date = Last Menstrual Period + 280 Days + (Cycle Length − 28 Days)
Naegele's rule assumes a standard gestation period of 280 days (40 weeks) from the first day of the last menstrual period (LMP). It adjusts the due date forward or backward if the user's regular cycle is longer or shorter than the average 28 days.
Worked Example
Here is a step-by-step example of how these values are calculated:
LMP Date
May 10, 2026
Cycle Length
28 Days
Result: Estimated Due Date: February 14, 2027. (If calculated today at 60 days post-LMP, gestational age is 8 weeks, 4 days in the First Trimester).
Frequently Asked Questions
How accurate is the estimated due date?
Only about 4% of babies are born on their exact due date. It serves as a general target window; most births occur within two weeks before or after the estimated date.
How does menstrual cycle length affect my due date?
Ovulation occurs roughly 14 days before your next period. If you have a longer cycle (e.g., 32 days), you ovulate later, meaning your due date is pushed back by 4 days compared to a 28-day cycle.