Pregnancy Week Calculator — weeks + prenatal schedule

How pregnancy weeks are counted

Pregnancy is measured in 'gestational weeks' starting from the first day of your last menstrual period (LMP), not from conception. This is the standard clinical convention. So 'six weeks pregnant' means six weeks since LMP, or about four weeks since conception (since ovulation typically occurs around day 14 of the cycle).

Each week consists of 7 days, so '8 weeks 3 days' means 8 × 7 + 3 = 59 days since LMP. Doctors typically write this as 8w3d or 8+3. The 'count' increments at midnight each day — your week-and-day might shift by one calendar day depending on when LMP started.

Trimesters and what to expect

First trimester (weeks 1-12 or 13): the most rapid embryonic-to-fetal development. Morning sickness, fatigue, and food aversions are common. Risk of miscarriage is highest in this phase. First prenatal appointment usually happens around 8-10 weeks.

Second trimester (weeks 14-26): often called the 'easier' trimester — many of the early symptoms ease. Anatomy ultrasound around 18-22 weeks. First fetal movements ('quickening') typically felt 16-22 weeks. Energy returns for many people.

Third trimester (weeks 27-40+): rapid fetal growth and lung maturation. More frequent prenatal visits. Common new symptoms: heartburn, swelling, sleep disturbances. Most births happen between weeks 38 and 42; only ~4% on the exact due date.

When the LMP-based estimate may be off

Irregular cycles (variations of 7+ days from one cycle to the next) make LMP-based counting less reliable. First-trimester ultrasound (8-13 weeks) measures the embryo and back-calculates a more accurate gestational age. Trust the ultrasound dating if it differs from LMP by more than a week.

IVF pregnancies use a different convention: due date = embryo transfer + 263 days (3-day embryo) or + 261 days (5-day blastocyst). The LMP method doesn't directly apply.

If you don't know your LMP exactly (typical for those with irregular cycles or who weren't tracking), an ultrasound at any point can establish gestational age.