Gestational Age Calculator

Gestational age is the number of weeks and days your pregnancy has progressed, counted from the first day of your last menstrual period (LMP). It is the universal standard used by obstetricians and midwives worldwide. A full-term pregnancy is 40 weeks (280 days) from LMP.

No. Gestational age is counted from LMP, which is typically about 2 weeks before conception. Fetal (embryonic) age counts from the actual date of fertilisation and is therefore about 2 weeks shorter. When doctors say '8 weeks pregnant', they mean gestational age — the embryo is about 6 weeks old.

Use the Conception Date mode in this calculator if you know (or have a good estimate of) when conception occurred. Alternatively, your healthcare provider will likely perform a dating ultrasound, which is most accurate between 8 and 14 weeks.

Gestational age calculated from LMP assumes a regular 28-day cycle with ovulation at day 14. Irregular cycles, late ovulation, or hormonal conditions can skew the estimate. Ultrasound measurements are typically more accurate before 14 weeks and may result in a revised due date.

The first trimester covers weeks 1–13 (conception through 13 weeks 6 days). The second trimester is weeks 14–27. The third trimester is week 28 onwards until delivery. Some definitions vary slightly — your provider may use slightly different cutoffs.