United Airlines just announced on Wednesday that, effective immediately, its MileagePlus frequent flyer miles will never expire. This means that members will be able to use their miles whenever they want to book flights, hotels or experiences, without having to pay a fee to reinstate expired points. Previously, members of United's MileagePlus program would see their miles disappear if there was no activity in their account for 18 months.

Previously, those who held United frequent flyer miles would be able to reinstate the miles, but for a fee. The cost to reinstate expired miles depended on the amount of miles the customer had. The fee started at $50 to reinstate 5,000 miles and went all the way up to $700 to reinstate 500,000 miles. This obviously angered many flyers, especially considering that in 2010, United merged with Continental Airlines, which had no mileage expiration dates.

The new rule went into effect on Wednesday, and members of United's frequent flyer program don't have to take any action.

This should be pleasing to customers of United, especially those who aren't frequent travelers. United isn't the first airline to make this change. In 2011, Delta removed expiration dates for its miles, and in 2013, JetBlue announced that TrueBlue points would never expire.

Most airlines still have expiration dates for their frequent flyer program miles or points. Southwest Rapid Rewards points expire if there is no activity for 24 months, though, card holders of the Southwest-branded credit cards can avoid this simply by using their cards. American Airlines Aadvantage miles expire after 18 months, too.

Adam Luehrs is a contributing writer at GET.com based in California. He likes traveling to new and exciting destinations, preferably on his credit card company's dime. When not on the road, Adam enjoys hiking around the mountains of San Diego, trying out new food and reading history books. Email: adam.luehrs@get.com.