Pregnancy Due Date Calculator
Estimate your delivery date and current pregnancy week from your last period.
About the Pregnancy Due Date Calculator
The AlarmDaddy Pregnancy Due Date Calculator estimates your expected delivery date using Naegele's rule — the standard method doctors use — based on the first day of your last menstrual period. It also tells you your current pregnancy week and trimester, and the estimated date of conception.
Enter the first day of your last period and your average cycle length (the default 28 days fits most people). The calculator adds 280 days (40 weeks) adjusted for cycle length and returns your estimated due date, how many weeks along you are today, and which trimester you are in. This is an estimate — only about 1 in 20 babies arrive exactly on the due date — but it is the same starting point every obstetrician uses.
How to use this calculator
- 1Enter the first day of your last menstrual period.
- 2Enter your average cycle length (default 28 days).
- 3Read your estimated due date, current week, and trimester.
The formula
Naegele's rule adds 280 days (40 weeks) to the first day of the last menstrual period, assuming a 28-day cycle with ovulation on day 14. The calculator adjusts for cycle lengths other than 28 days by shifting the assumed ovulation day.