McDonald's is giving away free fries. Here's how to get some.

Hollis Johnson

McDonald's French Fries.

• McDonald's is giving away free French fries on Friday, July 13 in celebration of National French Fry Day.
• Customers need to download and register for the McDonald's app, and then use the app to make a purchase.
• McDonald's isn't the only chain celebrating National French Fry Day on Friday. Dunkin' Donuts is selling "donut fries" for $2 for a limited time. And, Wayback Burgers is serving free bottomless fries with the purchase of a sandwich or burger.

McDonald's is giving away free French fries on Friday.

The fast-food chain is giving away free medium fries on Friday, July 13, as a National French Fry Day deal. Customers can get their free fries with any purchase of $1 or more.

The fine print: customers need to download and register for the McDonald's app, and then use the app to make a purchase. Customers can only make one order of fries on Friday.

McDonald's isn't the only chain celebrating National French Fry Day on Friday. Dunkin' Donuts is selling "donut fries" for $2 for a limited time. And, Wayback Burgers is serving free bottomless fries with the purchase of a sandwich or burger.

The origin of National French Fry Day is unclear. However, on July 13, it follows a number of other food "holidays" of dubious origin based around the promise of free food.

On Wednesday, July 11, 7-Eleven celebrated "Free Slurpee Day." On Tuesday, Chick-fil-A celebrated Cow Appreciation Day for the 14th year in a row, with customers dressing as cows for free food.

Fast-food chains are dealing with a competitive environment. To beat out rivals, chains are slashing prices and offering new deals to win over customers. Food "holidays" have served as a new maneuver from chains to get customers in the stores in recent years.