Before Mark Cuban became a billionaire, he spent his 20s struggling to make ends meet – Cuban frequently came home to his lights turned off, he had his credit cards cut and he worked a number of odd jobs to stay afloat.
It wasn't until Cuban sold his start-up, MicroSolutions, for $6 million in 1990 that he finally felt financially secure, he told Men's Health in an interview published Sept. 1.
But through the rough times, Cuban learned a few money lessons, and as a result, he has five key pieces of financial advice he shares.
"The secret to financial wellness is a couple things," Cuban told Men's Health.
Cuban has long advised against racking up credit card debt. So, he says, if you are going to use credit cards, pay the full balance on time.
"It's OK to use credit to buy a house – mortgage rates are so low and houses can appreciate in value, but you don't want to have a credit card that you don't pay off every month," Cuban told Men's Health. "The worst investment in the world is credit card interest."
Cuban learned this lesson the hard way in his 20s when the interest on the money he owed on his credit cards quickly accumulated.
"The hardest lesson I learned was getting my credit cards ripped up," he told Money in 2017. "I would charge something and think I would be able to pay it off and then not be able to. I can't tell you how many credit cards I had ripped up."
He understands it is extreme to avoid using credit cards all together, but insists it's important to pay off any balance.
"Using a credit card is okay if you pay it off at the end of the month," Cuban said in 2017. "Just recognize that the 18% or 20% or 30% you're paying in credit card debt is going to cost you a lot more than you could ever earn anywhere else."
(According to recent Federal Reserve data released in September, the average interest rate for all credit card accounts is 14.87%. Among accounts assessed interest, or accounts with outstanding finance charges, the average interest rate rises to 16.88%. But for consumers with credit scores below 670, interest rates can near 30%, CNBC Select reports.)
All in all, "paying off your credit cards after 30 days, or not even using credit cards, is the smartest investment you can make or not make," he said.
The "Shark Tank" investor's second tip is to "live like a student," he told Men's Health. That means avoid overspending and spending on things you can live without.
"You don't need to buy all this stuff, particularly when you cannot afford it," Cuban said. "The more money you can put in the bank, the better position you're going to be if something goes wrong."
Cuban learned the idea of "living like a student" from a book he read when he was just starting out: "Cashing in on the American Dream: How to Retire at 35" by Paul Terhorst, he told Money in 2017. The book encourages readers to live below their means.
"The whole premise of the book was that if you could save up $1 million and live like a student, you could retire," Cuban said of the book, which was published in 1988. "But you would have to have the discipline of saving. I believed heavily in that book. It was a big motivator for me."
Before the pandemic, Cuban typically recommended saving enough money to cover six months worth of expenses, he told Men's Health. But in today's climate, he recommends saving enough to cover your expenses for a year.
"Once you're able to save [for] a year of expenses, then you can start investing and putting it into something that can appreciate, like a low cost mutual fund or the Standard and Poor's Index," he said. (The S&P 500 index holds 500 of the largest U.S. companies.)
Indeed, experts often recommend the S&P 500 because it provides diversity at a low cost and generally delivers good long-term returns. (Warren Buffett told CNBC in 2017 that buying an S&P 500 low-cost index fund is "the thing that makes the most sense practically all of the time.")
People do not realize the power of negotiation, Cuban told Men's Health. "[N]egotiate the price down for things that you buy," Cuban said, (and you can even try negotiating your bills).
Cuban says using cash can be a powerful negotiation tool: "I tell people all the time, if you're out — you're going to take a yoga class and they want to charge you $30, say: 'Look, I've got 20 [dollars].' You know what, they're going to take it. Negotiating with cash is a far better way to get a return on your investment," he told Vanity Fair in 2017.
The self-made billionaire often negotiated when he was young and broke.
"I don't do that so much now," Cuban told Men's Health, as "people see me and the price goes up. But for the longest time, that's how I survived."
"Take advantage of deals on Amazon and other places where you can buy in bulk," Cuban told Men's Health, "because if it's money you're going to absolutely spend no matter what, and you can save 20%, 30%, 40%, that's the best investment you can make."
And it is easier to be a "smart shopper" than to invest in the stock market, he said.
"It's really hard to pick the right stock, or the right index fund, or the right mutual fund," Cuban said. "But if you, over the course of a year, typically spend $2,000 on all the consumables you use in your house, [like] your toothpaste, your toilet paper, shampoo, and you can save 40% on those by buying it [in bulk] and sticking it under your bed if you need to, that's $800 in savings."
"Sometimes, the best investment you can make is being a smart shopper," he told Men's Health.
Disclosure: CNBC owns the exclusive off-network cable rights to "Shark Tank."