Use the Due Date Calculator to estimate a due date from the first day of your last menstrual period. This is an estimate for planning, not a medical diagnosis.
How to Use
Choose the first day of your last menstrual period, then press Calculate. The result shows the estimated due date.
Formula in Plain Words
Add 280 days, which is 40 weeks, to the first day of the last menstrual period.
Worked Example
For a last menstrual period starting on January 1, 2026, adding 280 days gives an estimated due date of October 8, 2026.
FAQs
Is the due date exact?
No. It is an estimate, and the actual birth date often differs by days or weeks.
What if I do not know the LMP date?
This calculator needs that date. If you do not know it, a scan or a health professional can give a better estimate.
Why 280 days?
Because a typical pregnancy is counted as 40 weeks from the first day of the last menstrual period, and 40 weeks is 280 days.