How many weeks pregnant am I? Calculate it step by step
Calculadora de semanas de embarazo
Introduce la fecha de tu última menstruación
During the entire pregnancy, you discover surprising things, many changes occur in your body, and the baby evolves rapidly. Everything moves very fast, and that’s why one of the first questions on your mind as soon as the test confirms it is how many weeks pregnant am I. Let’s take it calmly so you can work it out for yourself and understand why your gynecologist counts in a way that at first seems a little odd.
How your gynecologist counts the weeks
One thing that caught my attention during my first pregnancy was the way my gynecologist counted the weeks. Typically, gynecologists start counting from the day of the last menstrual period and assume that the pregnancy will last 40 weeks. I knew the likely day of my conception, but he didn’t take it into account.
Our intuition for estimating our baby’s possible birth date would be from the day we think we got pregnant plus 38 weeks, which match 9 months. If we look closely, the two dates really do coincide: a woman usually ovulates about two weeks after her last period, and that’s where the two-week difference between the gynecologist’s count and ours comes from. By working it out this way, the gynecologist makes sure he has a starting point that leaves no room for doubt: the first day of your last period is always known with certainty, whereas the exact day of conception almost never is.
NOTE: Generally, a pregnancy is considered to last 38 weeks (40 counted from your period), but anything between week 37 and week 42 is considered normal.
What does “6 + 3” mean on your ultrasound?
Sometimes you might hear the pregnancy time given as two numbers, for example, 6 plus 3. If you look closely, on ultrasound scans, where the gestational age is worked out from the baby’s measurements, it’s shown that way. These two numbers are the pregnancy week plus the days: in the example above that’s 6 weeks and 3 days. We usually round up and speak only in weeks.
So, to sum up and following the format gynecologists use, when you ask yourself “how many weeks pregnant am I?” you count from the day your last period started up to today. That simple.
Pregnancy week calculator
To make it easier for you, since counting in weeks can be tricky, here is a pregnancy week calculator you can use to keep track of your pregnancy time.
Day of your last period: Pregnancy weeks:
If you still don’t know whether you’re pregnant, you can check with our free online pregnancy test, and if you want to be more sure you can see pregnancy test prices or dare to try a homemade pregnancy test at home.
And if, on top of knowing the weeks, you’d like to see it all on a spinning wheel just like your gynecologist’s, try our online gestogram: it shows your week, trimester and estimated due date with a simple spin.
A trick to keep track
If you find it impossible to count week by week, especially for our partners ;o), what I did was write the pregnancy week number in front of each week on the calendar we have on the fridge. That way, every day it’s just a quick glance—no maths needed.
And if you fancy a bit of fun in the meantime, try your luck with our fun fingerprint pregnancy test game: it’s only a game, not a real test, but it’s great to pass the time.
You might also find it useful to look at the first signs of pregnancy to make sense of what you’re feeling, or check what happens week by week in our pregnancy week by week section.
Frequently asked questions
What date do pregnancy weeks start from?
From the first day of your last period, which is how gynecologists count and how it’s shown on ultrasounds. That’s why they always ask you when your last period was.
Why does pregnancy last 40 weeks if it’s 9 months?
Because it’s counted from your last period, about two weeks before ovulation. Since conception, a real pregnancy is about 38 weeks. Both ways are valid—they just use a different starting point.
What does “week 6 + 3” mean?
It’s the pregnancy week plus the days: in this case 6 weeks and 3 days. It’s the format you’ll see on ultrasounds and in many pregnancy apps.
How many months is 12 weeks?
In general terms, 12 weeks is about 3 months. But because months don’t have the same number of weeks, the most reliable way is to talk in weeks and days, which is the reference your doctor uses.
What if I don’t remember my last period?
Don’t worry, it’s very common. Your gynecologist will work it out with an early ultrasound by measuring the baby, which is quite reliable during the first trimester. Tell him what you remember and he’ll adjust the date.
This article is for information only and doesn’t replace professional advice. If you have any concerns about your pregnancy, always consult your doctor or gynecologist ❤️.
