Pregnancy Due Date Calculator
Estimate your due date, gestational age, and conception date from your last menstrual period.
Enter your values to calculate your result.
Formula
Due Date = LMP + 280 days (Naegele's Rule) Conception Date ≈ LMP + 14 days
Naegele's Rule estimates a due date 280 days (40 weeks) after the first day of the last menstrual period, assuming a typical 28-day cycle. Conception is estimated at about 14 days after the LMP, around typical ovulation. Current gestational age is simply the number of days elapsed since the LMP, expressed in weeks and days.
Example
An LMP of January 1 gives an estimated due date of October 8 (280 days later) and an estimated conception date of January 15.
Frequently Asked Questions
How accurate is this due date?
Naegele's Rule is a widely used estimate, but actual delivery commonly varies by about ±2 weeks, and cycle length or an ultrasound-based estimate can shift the date. Your healthcare provider's estimate, especially from an early ultrasound, is more precise.
Why is gestational age counted from before conception?
Medical convention measures pregnancy from the first day of the last menstrual period, not from the estimated conception date — so at '4 weeks pregnant,' conception typically happened only about 2 weeks earlier.