How to use the Pregnancy Due Date Calculator
- Choose what you know: last period, conception or IVF transfer date.
- Enter the date (and your usual cycle length for the LMP method).
- See your estimated due date, weeks pregnant, trimester and milestones.
About this tool
Doctors usually estimate the due date with Naegele’s rule: 280 days (40 weeks) after the first day of the last menstrual period, assuming a 28-day cycle. If your cycle is longer or shorter, the date is moved by the difference — this calculator does that automatically. From a known conception date the due date is 266 days later; for IVF it’s calculated from the transfer date and embryo age.
Pregnancy weeks are counted from the last period, so at conception you are already about “2 weeks pregnant”. The first trimester runs to the end of week 12, the second to the end of week 26, and the third until birth. A dating ultrasound in the first trimester is the most accurate way to confirm the date.
Frequently asked questions
How is the due date calculated?
LMP + 280 days for a 28-day cycle (Naegele’s rule), adjusted by how much longer or shorter your cycle is.
How accurate is the due date?
It’s an estimate: most babies are born between 37 and 42 weeks. An early ultrasound gives a more reliable date.
Why am I counted as pregnant before conception?
By convention, pregnancy is dated from the first day of the last period, about two weeks before conception.
Is my information stored?
No. The calculation runs in your browser and nothing is saved or sent.