How Many Weeks Pregnant Am I? How to Calculate Gestational Age

How gestational age is counted in weeks and days from your last period, why it starts before conception, and how to calculate it yourself.

Gestational age is simply the number of days that have passed since the first day of your last menstrual period (LMP), or its equivalent if you're dating from conception or an IVF transfer, expressed in completed weeks and days.

The calculation

Days elapsed = today's date − LMP date. Divide by 7 for completed weeks, and the remainder is the extra days. For an LMP of January 1, 2026, checking on April 10, 2026 gives 99 days elapsed — 99 ÷ 7 = 14 remainder 1, so you'd be 14 weeks, 1 day pregnant.

Why gestational age starts before conception

It feels counterintuitive, but pregnancy is dated from the LMP by medical convention because that date is usually known precisely, while conception often isn't. Since ovulation typically happens around day 14 of a standard cycle, "4 weeks pregnant" really means only about 2 weeks since conception — the first two weeks of gestational age pass before conception has even occurred.

Gestational age vs. fetal age

Some sources distinguish "gestational age" (from LMP, the standard used by doctors and due date calculators) from "fetal age" or "conceptional age" (from actual conception, roughly 2 weeks less). If a pregnancy app or friend quotes a different week count than your doctor, this is almost always the reason — always go with your provider's dating, which is gestational age unless stated otherwise.

Enter your dates into the Due Date Calculator to see your current gestational age update automatically, along with how many days remain until your estimated due date.