Mathew Hughes, an 18-year-old high-school student in Marion, Ohio, has spent between $150 and $200 on the hugely popular videogame “Fortnite.”

That’s not a lot, he said, for an activity on which he sometimes spends four or five hours a day. Hughes pays for his expenses with money inherited from his late father, his gains on cryptocurrency investments and money made working at Panera and Arby’s. One of his friends has spent between $400 and $500, he said, and other players spend even more.

They’re not alone.

“I love this game and have a gambling addiction so I’ve probably spent $500-plus supporting it,” one commenter wrote on Reddit. There is even a term for superserious “Fortnite” players, who allegedly spend thousands. They are “whales.”

“Fortnite,” meanwhile, has been raking in cash. The game, which debuted in late 2017, made $233 million in March alone. It is a multiplayer third-person shooter game for mobile devices, personal computers and gaming consoles. (Epic Games Inc., which makes “Fortnite,” did not respond to a request for comment.)

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“Fortnite” is free to play, but serious players often end up spending money on cosmetic upgrades for their characters, including backpacks and different “skins,” Hughes said. You can also buy a “Battle Pass,” which gives players access to particular challenges; when you win a challenge, you gain access to new cosmetic items.

Mathew Hughes spends his own money on videogames, sometimes up to $1,000 on one game. Courtesy of Mathew Hughes

It’s easier than ever to spend money on games like “Fortnite.” And it doesn’t even feel like spending real money. Not at first, anyway. On “Fortnite,” players can buy 1,000 of the “V-bucks” virtual currency for $9.99. With that, they can buy items such as the “Battle Pass,” for 950 V-bucks. Outfits and skins cost between 500 and 2,000 V-bucks.

“ The games themselves are free to play, but the charges kick in later to make the games more exciting. ”

Extra charges are common among the most popular games, including the football game “Madden NFL,” the lifestyle role-playing game “Kim Kardashian: Hollywood” and the basketball game “NBA 2K.” And players don’t always stick to a single game: Hughes said he’s spent at least $1,000 on “NBA 2K.”

These games are part of a larger industry trend: The games themselves are free to play, but charges kick in later and can make the games more exciting. Sometimes, players need to unlock the ability to purchase extra items by reaching higher levels, so the extras they purchase can seem like rewards.

On “NBA 2K,” players can buy “virtual currency” for clothing and accessories, and additional skills. On “Madden NFL,” players can earn perks by completing objectives, but they can also use real money to buy some special features. (EA Sports EA, -1.98% , which makes the Madden games, and 2K TTWO, -2.35% , which produces “NBA 2K,” did not respond to requests for comment.)

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That business strategy may sound familiar if you’ve ever gambled at a casino, said Tim Barrett, a consultant at the research firm Euromonitor International. “Casino chips aren’t real money, and neither are gold coins on my videogame,” he said. Payment apps for Starbucks SBUX, -1.14% and Dunkin’ Donuts DNKN, +0.16% tap into this painless spending, he said.

“ Some games have protections in place to prevent children from racking up huge credit-card bills. ”

But before players know it, they may have spent far more than they’d realized they were spending. “The reality hits when you get your credit-card statement,” said Brendan Miller, a principal analyst at Forrester who covers payments. When consumers spend too much money, they may stop playing. So manufacturers have to find the psychological sweet spot, he said.

Some games have protections in place to prevent children from racking up huge credit-card bills. The Madden, FIFA and National Hockey League sports games from EA Sports, among others, have child accounts, that limit access to features, including any online access. Parents can also set spending limits for their children while using consoles like Sony’s SNE, -1.72% PlayStation 4.

It’s going to get easier to spend

Unfortunately for some consumers, payments are becoming even less painless. Many new innovations, including voice-activated payments, “chat bot” payments that allow customers to make purchases in messaging apps, and even payment systems in cars are designed to make consumers spend more.

Some gamers who can afford the array of charges say they’re worth ever dollar — or V-buck. Hughes said he isn’t worried that he’ll spend too much money or time on “Fortnite.” He said he likes having an unusual “skin” for his character. “You want to put yourself out there, like, ‘Hey, I’m good,’ and make the opponent a little scared,” he said.