Calculator
Pregnancy week calculator
Estimate gestational age on a selected date from the last menstrual period. Data is processed only in your browser, and the page explains the formula and limitations of the result.
Calculator
Enter data
The last menstrual period start and check date. Fields marked with an asterisk are required.
How to use the calculator
- Enter the required data: the last menstrual period start and check date.
- Check the values and select “Calculate”.
- Review the primary result and the detailed calculation components.
Calculation details
Formula and calculation method
Gestational age = complete weeks and remaining days from the first day of the last menstrual period; due date is approximately 280 days.
Worked example
At 73 days after the last menstrual period began, indicative gestational age is 10 weeks and 3 days.
Limitations
- Irregular cycles, uncertain dates and pregnancy development require clinician assessment and ultrasound dating.
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. Irregular cycles, uncertain dates and pregnancy development require clinician assessment and ultrasound dating.