If you’re trying to have a baby — or if you paid really, really close attention in sex ed and have a better memory than us — you may know there are lots of things that need to happen inside your body before you can get a big fat positive on a pregnancy test. The process goes like this:

  1. Your body releases a mature egg. (This is ovulation.)
  2. Sperm — either already in your body (since the little guys can survive up to 5 to 6 days in the uterus) or just making their grand entrance in the hours before ovulation — travel up the Fallopian tubes to meet the egg.
  3. A sperm fertilizes the egg — it really does only take one! (This is conception.)
  4. The fertilized egg travels down one of the Fallopian tubes to the uterus.
  5. The fertilized egg burrows, or implants, in the uterine wall. (This is implantation.)

Some of these steps happen in an instant — like conception — while others can take a day (ovulation) or even a week (we’re looking at you, traveling fertilized egg).

But implantation is especially key to getting a positive pregnancy test, so figuring out when it may occur (or if it already has) can help you decide whether it’s time to POAS (pee on a stick, as you’ll see in popular pregnancy forums).

This is because implantation triggers your uterus to start producing human chorionic gonadotropin (hCG), the “pregnancy hormone.” It’s the hormone home pregnancy tests detect to return a positive or negative result.

Let’s take a look at how to calculate your implantation date.

Related: How often does ovulation last each month?

A mature egg only has a window of about 12 to 24 hours after its release (ovulation) when it can be fertilized.

Once it’s fertilized, the egg’s journey down the Fallopian tubes can take anywhere from 6 to 12 days, but 9 days is average.

So if you know your ovulation date, here’s how you’d calculate your implantation date:

Date of ovulation + 9 days =
Date of implantation (give or take a few days)

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There are two ways you can do the calculation if you know this. These methods are less accurate than knowing your ovulation date, but they may still predict implantation for you.

Method 1: Figure out your ovulation date first

First, consider your average cycle length. Use that to calculate your approximate ovulation date:

Length of cycle – 14 days = Cycle day number for ovulation

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This calculation is used because the luteal phase (time after ovulation) is generally around 14 days, even if your cycle is longer than 28 days.

For example, if you have a 30-day cycle, you probably ovulated around cycle day 16. If you have a 34-day cycle, you probably ovulated around cycle day 20.

Add this number of days to the date of the first day of your last period. Using the corresponding date as your “known” ovulation date, use this ovulation equation:

Date of ovulation + 9 days =
Date of implantation (give or take a few days)

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Example: Say the first day of your last period (cycle day 1) was May 2. Your cycle length is usually 30 days. This means you may have ovulated on 30 – 14 = cycle day 16, or May 17. Your expected implantation date would be around May 17 + 9 days = May 26.

Another way to get your date of ovulation is to use our ovulation calculator retrospectively.

Method 2: Use (somewhat) standard averages

This method assumes you ovulate around cycle day 14 and it takes around 9 days for the fertilized egg to travel to the uterus. It’s based on a 28-day cycle.

Date of first day of last period + 23 =
Date of implantation (give or take a few days)

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This method is the least accurate because not all women ovulate on the 14th day of their cycle.

If implantation did occur, your body will start producing hCG. However, this has to build up a little bit before a home pregnancy test will detect it. So your best bet is to wait at least 3 to 4 days after implantation to test.

Most accurate? Wait until after your missed period. For most women, this will be pretty close to 5 to 6 days after implantation. But we get it — when you’re trying to conceive, going even a day longer without knowing can be absolutely excruciating.

If you do test before your missed period, just know that you may get a negative result and still be pregnant. Give your hCG time to build up more, and then test again a couple days later.

No implantation calculator is going to be exact, because every body and every pregnancy is unique. But these calculations can help you estimate when you may have implantation symptoms and when you can take a pregnancy test.

Your estimated implantation date may also help you figure out if you’re starting your period or having implantation bleeding.

Regardless of whether you get pregnant this cycle, take heart. It usually takes a few tries.

If you’ve been trying longer than a year (or longer than 6 months if you’re over age 35), talk to your doctor. They can help diagnose any issues that might be preventing pregnancy and discuss options for growing your family.