Gestation Age Calculator

Compute gestational age (weeks + days) from last menstrual period. Not medical advice.

Result

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How to use this calculator

Enter the LMP date.
Set "as of" to today (default) or any reference date.
Read weeks + days plus trimester.

About this calculator

Gestational age is conventionally measured from the first day of the last menstrual period (LMP), not from conception (which happens ~2 weeks later). A "term" pregnancy is 38-42 weeks gestational age. This calculator is a formula tool only — pregnancy decisions should be made with a qualified medical professional.

Frequently asked

LMP vs conception?+

LMP is ~2 weeks before conception. Gestational age (LMP-based) is what hospitals and OBs use; embryonic age (conception-based) is 2 weeks less.

When are the trimesters?+

1st: weeks 0-12. 2nd: 13-26. 3rd: 27-birth (typically week 38-42).

Is this calculator medical advice?+

No. It's a date-arithmetic tool. Pregnancy decisions, anomaly screening, prenatal care timing — work with a qualified OB/GYN or midwife.

What if I don't know my exact LMP?+

Estimate to the best of your ability; ultrasound dating is more accurate after week 7 and is the clinical standard when LMP is uncertain.

Can this predict due date?+

See due-date-from-conception (266 days from conception, ~280 days from LMP). Many calculators add 280 days to LMP for the estimated due date.

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Exact age in years, months, days, hours, and minutes — plus countdown to next birthday.