Reproductive Health Calculators
Pregnancy Conception Calculator
Estimate conception and last-period dates from an estimated due date.
ResultEstimated conception date: October 27, 2025
Estimated last menstrual period: October 13, 2025.
How to use this calculator
- Enter the estimated due date supplied or reviewed by a maternity professional.
- Review the live result and use Copy result when you need to share it.
How the calculation works
The tool subtracts 266 days for conception and 280 days for menstrual dating.
Formula
The tool subtracts 266 days for conception and 280 days for menstrual dating.
Step-by-step calculation
- Enter the estimated due date supplied or reviewed by a maternity professional.
- The tool subtracts 266 days for conception and 280 days for menstrual dating.
- Check the displayed result, then copy it if needed.
Worked example
A due date of 20 July estimates conception about 266 days earlier.
Risk guidance
Frequently asked questions
Does this tool send my inputs anywhere?
No. The interactive calculation runs in your browser and this site does not submit tool inputs to a backend.
How should I use the result?
Check that the entered units and values match your situation, especially around dates, breaks, and rounding.