Calculate your estimated due date, gestational age, trimester timeline, and baby milestone dates from your last menstrual period or conception date with our calendar tracker.
A typical pregnancy lasts approximately 280 days (40 weeks) from the first day of the last menstrual period (LMP). Our free online Pregnancy Due Date Calculator estimates your baby's due date, your current gestational week, the remaining days until delivery, and details your progress through the three trimesters.
The calculation is based on Naegele's rule, which estimates the due date by adding one year, subtracting three months, and adding seven days to the first day of your last menstrual period. While this gives a reliable estimation, only a small percentage of babies are born on their exact due date.
The due date is typically calculated by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP). Lenders/Doctors use this standard because the exact date of conception is often unknown.
Naegele's rule is a standard method of calculating the due date. The formula is: Date of LMP + 7 days - 3 months + 1 year. This assumes a regular 28-day menstrual cycle.
The first trimester lasts from week 1 to the end of week 12. The second trimester spans from week 13 to week 26. The third trimester starts at week 27 and lasts until birth (approx. week 40).
Only about 4% to 5% of babies are born on their exact estimated due date. Most are born within a two-week window before or after the due date, which is considered full term.