Due Date Calculator
Estimate a due date using last-period and cycle information.
Estimated conception date: August 3, 2026.
Clinical ultrasound dating may change the estimate.
How to use this calculator
- Enter the first day of the last menstrual period and average cycle length.
- Review the live result and use Copy result when you need to share it.
How the calculation works
Menstrual dating adds 280 days and adjusts for cycles longer or shorter than 28 days.
Formula
Menstrual dating adds 280 days and adjusts for cycles longer or shorter than 28 days.
Step-by-step calculation
- Enter the first day of the last menstrual period and average cycle length.
- Menstrual dating adds 280 days and adjusts for cycles longer or shorter than 28 days.
- Check the displayed result, then copy it if needed.
Worked example
A 30-day cycle shifts the basic 280-day estimate two days later.
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.
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