Calculator
Estimated due date calculator
Estimate a due date from the last menstrual period or conception date. Data is processed only in your browser, and the page explains the formula and limitations of the result.
Reviewed: 3 August 2026Processed locally
Calculator
Enter data
The type of known date and reference date. Fields marked with an asterisk are required.
How to use the calculator
- Enter the required data: the type of known date and reference date.
- Check the values and select “Calculate”.
- Review the primary result and the detailed calculation components.
Calculation details
Formula and calculation method
Due date = first day of last menstrual period + 280 days, or estimated conception date + 266 days.
Worked example
For a last menstrual period beginning on 1 January, the indicative due date is 280 days later in early October.
Limitations
- This is a statistical estimate; clinical dating uses cycle history and ultrasound findings.
Sources
Engine version: 1.0 · Last reviewed: 3 August 2026
Frequently asked questions
Is the entered data sent to a server?
No. The calculation runs locally in your browser and the values are not saved by default.
Is the result definitive?
Not always. This is a statistical estimate; clinical dating uses cycle history and ultrasound findings.