HEALTH RESULT
Result
Review the estimate based on the information you entered.
Result Overview
Key resultUse the estimate as an informational reference.
Result at a Glance
Key detailsAbout this tool
Pregnancy Calculator
Estimate pregnancy dates from a last menstrual period, estimated due date or conception date, including an approximate gestational timeline.
Learn how pregnancy dating estimates are built from the last menstrual period, conception timing and a typical 40-week gestational model.
How pregnancy dating works
Gestational age is commonly counted from the first day of the last menstrual period rather than from the actual conception date. That convention is why the expected delivery date is roughly 40 weeks from LMP.
Using the last menstrual period
For a standard 28-day cycle, the model adds about 280 days to the first day of the last period. A different average cycle length can shift the estimate.
Using conception date
If conception timing is known, an estimated due date is commonly modeled as about 266 days later.
Why the date is an estimate
Ovulation, implantation and cycle length vary. Ultrasound dating may be used clinically when appropriate.
How to use the result
Enter the dating information you know and review the estimated due date and gestational age. Do not treat the calculation as proof of fetal age or a medical diagnosis.
Health note
Pregnancy dates are clinically important. Use your healthcare provider’s dating assessment for medical decisions.
Related Health Tools
Explore related Tervilo calculators for a broader view of the same topic.
Questions & Answers
Frequently Asked Questions
What does the Pregnancy Calculator calculate?
It provides an estimate from the inputs you enter. Review the detailed guide on this page for formulas, interpretation, assumptions and limitations.
How is an estimated pregnancy due date calculated?
A simplified calendar model uses about 40 weeks from the last menstrual period, with adjustments for cycle length. Conception-based dating uses about 266 days from conception.
Why can a pregnancy due date change?
Ovulation timing, cycle variation and clinical dating information can change the estimated date. A calculator result is only an approximate calendar estimate.
Should I use a calculator instead of clinical pregnancy dating?
No. Use it for general information and planning. Clinical pregnancy dating can use additional information and should guide medical decisions.