Pregnancy Calculator
Estimate due date, current pregnancy week, and trimester based on the last menstrual period (LMP).
Inputs
Result
Enter values on the left and select Equals to see the result here.
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What the Pregnancy Calculator does
- Estimates due date using a standard 280-day (40-week) pregnancy length.
- Calculates current pregnancy week and trimester for today’s date.
How to use the Pregnancy Calculator
- Enter the start date of your last menstrual period (LMP).
- Click Calculate to see the estimated due date and pregnancy week.
Formula / methodology used
- Due date uses Naegele’s rule: LMP + 280 days.
- Current week is calculated from days since LMP, then grouped into trimesters.
Example calculation
LMP start date: 2026-01-01.
- Due date = 2026-01-01 + 280 days
- Compute weeks since LMP for today
Result: Outputs estimated due date, week number, and trimester.
Pregnancy Calculator FAQs
Is the due date exact?
No. It’s an estimate. Many births occur before or after the calculated date.