Here's where you can snag free donuts for National Doughnut Day

It's National Doughnut Day, and there are a ton of sweet deals.

For businesses, it's an easy way to cash in. Fast food historically has been a low-profit business with little customer loyalty. So, chains unveil big giveaways, typically tied to their mobile apps, to help drive business and garner repeat customers.

"National (insert food here) Days" expand beyond doughnuts, including coffee, cheeseburgers and ice cream giving chains a boom in business and sparking publicity.

The 86-year-old tradition is celebrated on the first Friday in June. It was started by the Salvation Army in Chicago in 1938 to honor the group's "donut lassies," who served treats and provided assistance to soldiers (the "doughboys") on the front lines during World War I.

Doughnuts have been around since long before the First World War, and we have the Dutch to thank for them. The Dutch would make "olykoek," which translates to oily cake. The first Dutch doughnuts didn't have a hole, but they were fried in hot oil and the dough was sweet.

Enough of the boring stuff, here's where to get free doughnuts:

Dunkin'

Customers can get a free doughnut with a purchase of a beverage on Friday.

Dunkin' has also partnered with the appropriately named singer Jelly Roll to celebrate the holiday with doughnut-themed merchandise on its website. It's also selling a limited-edition doughnut-shaped sponge for $9.98 it produced with Scrub Daddy.

Krispy Kreme

The chain is making it easy to celebrate: Any of its regular doughnuts, like glazed or cake, are free with no purchase necessary. (It's limited time Dolly Parton-themed treats are excluded.)

Plus, it's selling a dozen of its glazed doughnuts for just $2 with the purchase of a regularly priced dozen of doughnuts.

Sheetz

The convenience store and gas station chain with more than 700 locations is offering one free doughnut with a purchase of a coffee, with the deal lasting until Sunday. The offer is only available in its app.

7-Eleven

Members of its 7Rewards loyalty program get to buy a glazed doughnut for $1 on Friday, with the offer also valid at Speedway and Stripes locations.

Duck Donuts

You can get a free cinnamon sugar donut on Friday.

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