How Far Along Am I?

How pregnancy weeks are counted

Here’s the part that confuses almost everyone: pregnancy is counted from the first day of your last menstrual period (LMP), not from the day you conceived. This number is called your gestational age, and it’s the standard every doctor, midwife, and pregnancy app uses.

Because ovulation and conception usually happen about two weeks after your period starts, the clock is already ticking before the baby exists. In practical terms, that means you are counted as roughly 2 weeks pregnant on the day of conception itself, and about 4 weeks pregnant by the time your next period would have been due. So “6 weeks pregnant” really means the embryo has been developing for about four weeks — the extra two weeks are baked into the counting method. It feels strange, but it gives everyone a single, shared starting point that doesn’t depend on knowing the exact moment of conception.

How the calculator works

You enter the first day of your last period, and the calculator does the rest. It counts the days that have passed since then and converts them into completed weeks plus leftover days, shown as “weeks + days” (the same format your provider uses, like 12 weeks and 4 days).

• How far along — your current gestational age in weeks and days.
• Trimester — which of the three stages you’re in right now.
• Due date — estimated as your last period plus 280 days (40 weeks), the standard Naegele’s-rule estimate.
• Progress — how far through the full 40 weeks you’ve travelled, so you can see what’s ahead.

Everything runs in your browser — nothing you type is sent anywhere or stored.

The three trimesters

Pregnancy is split into three stretches, each with its own milestones:

• First trimester (weeks 1–13): the embryo’s major organs form, the heartbeat begins, and early symptoms such as nausea and tiredness are often at their strongest.
• Second trimester (weeks 14–27): many people feel their best here. You’ll usually feel the first movements (“quickening”), and the anatomy ultrasound happens around week 20.
• Third trimester (weeks 28–40): the baby grows fastest, appointments become more frequent, and you’ll start preparing for birth.

Weeks vs months

People often say pregnancy lasts nine months, but it’s usually described in weeks — and the two don’t line up as neatly as you’d expect. A full-term pregnancy runs about 40 weeks from your last period. If you divide 40 weeks by the four weeks in a calendar month, you get roughly ten months, not nine.

The reason is that calendar months are longer than four weeks — most have 30 or 31 days, so they average about 4.3 weeks each. Forty weeks works out to a little over nine calendar months, which is where the familiar “nine months” figure comes from. Weeks are simply more precise, so providers track your pregnancy week by week rather than month by month.

How accurate is this estimate?

This tool gives a planning estimate based on the date you enter and a standard 28-day cycle. If your cycles are longer, shorter, or irregular, your true gestational age can differ by a week or more, because ovulation didn’t happen on the assumed day 14. The most accurate way to confirm how far along you are is an early dating ultrasound before 14 weeks, which measures the baby’s size directly and often becomes the official date your provider uses.

Want to see what’s happening at your stage? Our pregnancy week-by-week guide walks through each week’s development and what to expect.