For any woman on the road to motherhood, a pregnancy test is one of the most important markers along the journey. From finding out, to confirming, to using it as a fun way to surprise your loved ones, pregnancy tests are a centerpiece.

Luckily, these game-changers are easy to use and widely available. But for any woman stocking up, a common question may have crossed your mind: Can pregnancy tests expire? And if they do, can you still trust the result?

Determining whether or not you’re pregnant is crucial information, and it’s one you want to be sure about. A false negative or a false positive, though not uncommon, can be heartbreaking. Here’s a breakdown of how these tests work, how accurate they really are, and what happens if they’re past their prime.

How Do Pregnancy Tests Work?

Pregnancy tests work by detecting a hormone called human chorionic gonadotropin, commonly known as hCG, in your urine. This hormone is only produced after a fertilized egg attaches to the uterus, which is typically around 6–12 days after conception.

Most home pregnancy tests are urine-based sticks with chemicals designed to react when hCG is present. If the hormone is detected, you’ll see a second line, a plus sign, or a digital “pregnant” message, depending on the brand of pregnancy stick. If there’s no hCG detected, you’ll simply get a negative response.

While the science is intricate, the process is luckily very simple: pee on the stick, wait a few minutes, and read the result.

How Accurate Are Pregnancy Tests?

So, can you really trust your home pregnancy test? Very much so, since they are up to 99 percent accurate when used correctly and after a missed period. However, the timing and technique make all the difference, so it’s important to be intentional.

Here are a few tips to get the most accurate result from your at-home pregnancy test:

  • Wait until after your missed period. Testing too early can give you a false negative.
  • Use the first urine of the day. It usually has the highest concentration of hCG.
  • Follow the instructions exactly. Every brand has slight differences, so read the label.
  • Don’t check the results too late. Reading a test after the recommended time can lead to evaporation lines, which might look like a faint positive.

As always, if you’re still unsure, you should take a second test or check in with your doctor for a blood test. Those tend to be even more accurate.

Do Pregnancy Tests Expire?

Yes, pregnancy tests do expire. Usually that’s within two to three years from the manufacture date.

“Like any medical product, pregnancy tests have a shelf life,” says Dr. Laura Purdy, board-certified family medicine physician. “Over time, the chemical that detects hCG can degrade, which makes the test less reliable.”

Over time, the chemical reagents in the test can break down, making them less reliable. This means that an expired test might show a false negative, offer inaccurate or unclear results, or simply not react at all.

“Expired pregnancy tests aren’t dangerous, but they can give you inaccurate results,” explains Dr. Mary Jane Minkin, OB-GYN and clinical professor at Yale University. “For the most reliable answer, always check the expiration date and follow the test instructions carefully.”

This is why it’s important to always check the expiration date on the box before using a test, especially if you’ve had it stocked up in your cabinet for a while. It’s always worth picking up a new one when it comes to taking a test, as it’s better to be safe and sure.