Before calculating
Prepare First day of last menstrual period and Calculate on. Match each input to the document, measurement, or current source you are using. Keep units, dates, currency, and time periods consistent.
HEALTH REFERENCES WITH CLEAR LIMITS
Pregnancy Week Calculator
Estimate completed pregnancy weeks between the first day of the last menstrual period and a selected date.
Review your result
Your result
Ready when you are.
Enter your values and select Calculate. Your result stays on this device.
How it works
Completed pregnancy weeks are counted from the first day of the last menstrual period to the selected date.
Assumptions
This is a calendar estimate and may differ from clinical dating.
Use case
pregnancy week calculator: a clear planning check
Estimate completed pregnancy weeks between the first day of the last menstrual period and a selected date. The stated formula, assumptions, and result limits remain visible so the calculation can be checked in context.
Use a clear pregnancy week calculator scenario with values you can verify before relying on the result.
Build a reliable scenario
How to use and verify your Pregnancy Week Calculator result
Pregnancy Week Calculator helps you check a specific health & family question with figures that apply to you. Estimate completed pregnancy weeks between the first day of the last menstrual period and a selected date. Estimate completed pregnancy weeks between the first day of the last menstrual period and a selected date. The stated formula, assumptions, and result limits remain visible so the calculation can be checked in context. Use a clear pregnancy week calculator scenario with values you can verify before relying on the result. The page keeps the method and limits visible so the result can be understood, compared, and checked instead of treated as an unexplained answer.
What changes the result?
The stated method is: Completed pregnancy weeks are counted from the first day of the last menstrual period to the selected date. Change one assumption at a time to see which input drives the result, then compare scenarios on the same basis.
When checking the answer
This is a calendar estimate and may differ from clinical dating. This is educational information only and not a substitute for prenatal care or a clinician’s dating assessment.
Quick verification checklist
- • Confirm the date and unit of every input.
- • Replace defaults with values that match your case.
- • Compare the answer with a second scenario.
- • Use the official source for regulated or high-impact decisions.
Source and update
Last reviewed: 2026-08-10
ACOG — methods for estimating the due dateFrequently asked questions
Is Pregnancy Week Calculator free to use?
Yes. This calculator runs in your browser and does not require an account.
Is the result guaranteed?
This is a calendar estimate and may differ from clinical dating.
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