A person counting coins while adding up their savings on a calculator. - Garun Studios/Shutterstock

Canadian venture capitalist and seasoned “Shark Tank” investor Kevin O’Leary is known for dolling out no-holds-barred financial opinions. He’s made deals on products all over the spectrum, from pet DNA tests and gym equipment to cryptocurrency and wine, and it’s come with plenty of often-strict advice to partners and aspiring entrepreneurs along the way. But while O’Leary has built an entire career out of making bold financial moves, the self-made millionaire tends to keep his tips surprisingly simple when it comes to advising his own family members. In a recent video posted to his social accounts, O’Leary said, “What piece of advice do I give my kids over and over and over again about money? Don’t spend it. Save it, invest it, let it compound. That’s the gift the market gives you.” Specifically, he says to set aside 15% of all earnings (including gifts and any extra cash) for investment.

This might not be O’Leary’s secret to earning $1 million fast but a well-worth it payoff over time. O’Leary concludes this advice by noting that the average income in the U.S. is $68,000, so if you do this your whole life, you’ll wind up a millionaire by the time you hit retirement at 65. This is in line with the businessman’s previous statements over the years, in which he’s advocated against “wasting money” on things like fancy coffees and going out for lunch and urged people to save.

Read more: 11 Warning Signs You’re Not Financially Ready To Retire

A person putting money into a piggy bank while calculating their savings. - Garun Studios/Shutterstock

Kevin O’Leary’s financial tips seem simple enough, but since he’s talking about becoming a millionaire here, is it really sound advice? That depends. First, O’Leary’s reasoning is based on a supposed average income of $68,000. For simplicity’s sake, let’s say you earn that over a period of 20 years and put 15% every year in investments. That’s $10,200 a year, adding up to $204,000 put away over two decades. JP Morgan Chase has the average market return rate around 10%, so that would be a minimum return of $1,020 annually or $20,400 over two decades. Compounded over time as your balance (and likely, your income) grows, and that could indeed push your assets to over a million.

Still, incomes vary wildly, as does cost of living. Average income also fluctuates between data sets. For example, the Social Security Administration estimates the average salary to be $63,932.64, while SOFi pegs it just slightly higher at $66,672. The Pew Research Center meanwhile shows that the income for middle class U.S. households falls anywhere between $56,600 to $169,800, with social class (lower, middle, and upper) being dictated by income level combined with regional living costs. Individual expenditure needs vary, and not everyone may be able to set aside 15% each year, especially if medical debt or other unexpected costs arise. But if you can comfortably set aside 15% each year, it’d be wise to go ahead and do so, adjusting as needed over time.