Are your Pokémon cards worth millions? Here's what to look for.

With Pokémon's 30th anniversary being Feb. 27, here's what to know about authenticating your cards to determine their worth.

Fans of Pokémon growing up might have thousands of dollars sitting in storage somewhere.

As nostalgic fans celebrate Pokémon's 30th anniversary, with Pokémon Day honored on Friday, Feb. 27, they might feel the urge to dive into their past collections of Pokémon trading cards and collectibles.

They also might be surprised to learn that those cards could hold more value than just childhood memories, authenticators say, with some rare editions reselling for thousands.

For fans tempted to peek back at their old collections, here's how to determine whether your old Pokémon trading cards could earn you some money.

Before learning the prices of collectible Pokémon cards, fans need to authenticate and grade them, which means an expert must examine the cards to determine how close they are to "perfect" condition via a designated grading scale that often goes from 1 to 10. The higher the grade, the higher the potential price it can sell for.