'Shark Tank' star Kevin O'Leary once said buying lunch or coffee is like burning money — and risks delaying retirement

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• Buying lunch or a cup of coffee is a stupid waste of money, Kevin O'Leary says.
• The "Shark Tank" star says little treats hurt people's savings and can even delay their retirement.
• "You go to work, you spend $15 on a sandwich — what are you, an idiot?" he said on a podcast.

Lunch bowls, cups of coffee, and other little indulgences might seem harmless. But the costs add up quickly and leave less money to invest, which can ultimately force people to delay retirement because they haven't saved enough, Kevin O'Leary says.

In "Cold Hard Truth on Men, Women & Money," O'Leary spelled out the dangers of squandered cash. "Ghost Money is dead money, money wasted on stupid things, money that should have been invested instead," he said in the 2012 book, complaining about "how casually money is flushed down the toilet."

The "Shark Tank" investor and O'Leary Ventures chairman calculated that someone who spends $10 a day on cigarettes, $12 a week on coffee, $8 a week on magazines, and $200 a month on lunches for 20 years has effectively "set fire to" about $276,000, assuming they could have earned a 6% compounded annual return on their money instead.

"If you spend a wad of cash on cappuccinos and magazines in your twenties, there's a good chance you'll be serving coffee or working in a magazine stall in your seventies to pay for your retirement," he said.

Fewer people buy magazines now, but in O'Leary's example, they could easily be substituted for streaming subscriptions or food deliveries. He advised cutting out impulse purchases and parking the resulting savings in a dedicated investment account, as people find it easier to give up bad habits when they can see their balances grow.

O'Leary, the self-proclaimed "Mr. Wonderful," is known for being blunt about bad ideas and frank in his feedback. He scolded money-wasters on the "Erika Taught Me" podcast last year, a clip of which he shared on Instagram in September.

"Stop buying coffee for $5.50," O'Leary said, bemoaning that 15% to 20% of many people's daily spending is on "stupid stuff."

"You go to work, you spend $15 on a sandwich — what are you, an idiot? It costs you 99¢ to make a sandwich at home and bring it with you," he said. "You start to add that up every day, it's a ton of money."

O'Leary added that young people just starting their careers in cities often "piss away about $15,000 a year" when they're not earning much, and being so frivolous can lead to financial troubles.

The celebrity investor has shared plenty of personal finance tips over the years. He's recommended treating purchases like investments, warned against lending to family, advised couples to keep their finances separate, and told people to get married younger and have more kids.