Pregnancy Calculator
Estimate gestational weeks and days, approximate stage and due date from the first day of the last menstrual period (LMP) and an as-of date.
Calculator arithmetic runs locally in your browser and does not require an API.
The interactive calculator loads here when JavaScript is enabled.
How to use Pregnancy Calculator
Enter the first day of LMP and the date for which you want the estimate. The as-of field starts with today on your device. The input range is a tool limit, not a clinical assessment.
Formula and method
Gestational days = as-of date − LMP. Divide by seven for completed weeks and remaining days. Estimated due date = LMP + 280 calendar days, assuming a regular 28-day cycle.
Understanding the results
Gestational age is counted from LMP, rather than the assumed conception date. Approximate stages use 14- and 28-week boundaries. Irregular cycles and clinical findings can change dating; the tool does not confirm pregnancy or replace care.
Worked example
With LMP January 1, 2024 and as-of March 1, 2024, 60 calendar days have elapsed: 8 weeks and 4 days. This model gives an estimated due date of October 7, 2024.
Pregnancy and conception dates are estimates. A healthcare professional can provide guidance based on your individual situation.
References
Frequently asked questions
Does the calculated age confirm pregnancy?
No. It performs date arithmetic from the dates entered and cannot establish pregnancy status.
Why can clinical dating differ?
Cycle timing, uncertainty about LMP and ultrasound findings can affect the clinical estimate.
Can I calculate for a date other than today?
Yes. Change the as-of date to inspect the model on that date, within its supported range.