How Far Along am I? How to Work it Out

Once you have that positive pregnancy test, the next question you probably have is: how far along am I?

There’s nothing quite like working out when will baby be due and popping it in your calendar to start the countdown!

But counting pregnancy weeks can be a confusing game—one that’s important to get right so you schedule scans, tests, and appointments for the right times.

Forget the pressure, let’s get your answers to that burning question: How many weeks pregnant am I?

Here’s how to work it out.

In this article: 📝

How do I know how many weeks pregnant I am?

So the (slightly) weird thing about how far along you are is that the 40 weeks of pregnancy actually starts before you’re technically pregnant.

What's referred to as gestational age.

Determining how far along you are in pregnancy starts with remembering the first day of your last menstrual cycle (LMP).

By this, we mean the first day of real bleeding, not the day or two of spotting that can happen prior.

That day is day one of pregnancy.

By counting forward from that day, you can work out how many weeks pregnant you are and what your due date might be.

Never has a calendar been more exciting!

Why does pregnancy go by your last period?

The short answer? It's because the exact moment of conception is often a mystery.

But when you're pregnant, doctors need a solid starting point to figure out when your baby will likely arrive so they can be sure the developmental milestones are being reached at the right time.

And they use the first day of your last period to do this—not when the baby was actually made—because most people don't know exactly when that happened.

It's like marking the start line in a race on a day that's easy to remember.

This simple method is called Naegele’s Rule.

All you do is take that start date—the first day of your LMP—add nine months to it, and then add seven more days.

This gives you an estimated due date, which is just a best guess for when your baby might come.

How am I 4 weeks pregnant if I conceived 2 weeks ago?

It all comes down to Naegele’s Rule being based on a 28 cycle.

Basically, the assumption is that you ovulate (when an egg is ready to meet sperm) about 14 days after your period starts and that the majority of women have a 4-week menstrual cycle.

Spoiler alert: We don't.

Studies show that only around 12% of women actually fit into this neat little box.

It's also worth remembering babies have their own schedules, and they might arrive a bit before or after that date.

Still, it's a simple way for everyone to get ready for the big day, even if it's not super precise.

And it helps your doctor keep track of how things are going throughout your pregnancy.

How to know how far along you are in pregnancy?

The pregnancy calculator of choice tends to use Naegele's rule formula.

Basically, once you have the date of the first day of your last period, you can calculate a number of key dates.

It looks like this:

• Two weeks ahead from that date is probably when ovulation and fertilization happened
• The number of weeks that have passed since the first day of your last period is how far along you are now. Yay!
• 40 weeks (280 days) from the first day of your last period will be your estimated due date. Eep!
  This means by the time you have missed a period, you are considered around 4 weeks pregnant.

How to calculate your due date?

How to calculate how far along you are (and when baby is due to debut) can depend on a few key dates (if you know them).

1. Due date calculator by ovulation

Knowing the exact date of ovulation can help, as usually ovulation and fertilization happen on (or around) the same day.

If you have a very regular menstrual cycle and signs like ovulation pains, or if you’re using ovulation tests, you might know exactly when you ovulated.

Generally speaking, based on a 28-day cycle, you ovulate around day 14 of your cycle (14 days after the first day of your period).

But remember, if you have longer/shorter/irregular cycles—which may well be the case—this number might not be the same for you.

2. Due date based on day of sex

If you only had sex once since your menstrual cycle and around your fertile window, fertilization likely happened 1-5 days after that.

So remembering this date can help with accuracy, too.

3. How to calculate due date with IVF

If you’re using assisted fertility methods to get pregnant, like an IUI (intrauterine insemination) or IVF embryo transfers, your specialists will have all your dates tracked.

4. Due date calculator by ultrasound

Throughout pregnancy, you'll probably have at least one ultrasound scan, which can also help determine the dates of your pregnancy by tracking the size of the fetus.

Usually, around 10-14 weeks, you will have an ultrasound called a dating scan.

This calculates how far along you are in pregnancy and checks on the baby’s development along with estimating your due date.

Using ultrasound measurements, the sonographer will be able to make an accurate assessment of your gestational age.

Amazing!

And hey, when in doubt, you can always use our expert pregnancy due date calculator

Do you have symptoms at 4 weeks pregnant?

4 or 5 weeks is a common time to find out you’re pregnant since that’s the time your period would have shown up.

If you’re eager to start feeling all those pregnancy feels, you might wonder if you should be having some early pregnancy symptoms, and at 4 weeks pregnant, you just might.

As soon as you are 1 to 2 weeks from fertilization (so, 3 to 4 weeks from your last period), you may feel more tired than usual, some breast tenderness, and the onset of pregnancy nausea and vomiting.

First trimester symptoms can come as a bit of a shock, but you know what?

You’ve got this mama.

Welcome to pregnancy! 🎉

The Peanut mamas have got you 🫶