It was after going through some old financial statements that Samara Fields realized that, for several months while at university, she had been taking cash advances from her credit card, instead of withdrawing the funds from her bank account.
Ms. Fields estimates she paid at least $1,000 in interest charges from those cash advances.
"I didn't realize what I was doing. ... I was completely naive," says Ms. Fields, 30. "I racked up the debt pretty quick."
She grew up in a small town, Snow Lake, Man., where most people paid for everything in cash. When she went to the University of Manitoba in her early 20s, having a credit card was a new experience.
Ms. Fields acknowledges she didn't know enough about how to use it – and how not to.
"Nobody ever told me," she says. "It would have been smarter to use the credit card to pay for things, instead of taking out the cash," or withdrawing money from her savings account instead.
The misuse of credit cards is a common mistake among millennials (and likely for young people from generations before them), as they start to spend and earn their own money.
Jonathan Rivard, a financial adviser at Edward Jones, says many millennials don't understand the long-term impact compound-interest charges have on debt.
"It's one of the biggest mistakes I see," says Mr. Rivard, who is based in Richmond Hill, Ont. He sees it on everything from credit card debt to auto loans.
"They need to think about the impact of these decisions over a longer period of time, in terms of interest."
Another mistake is taking on too much debt, without a plan to pay it off, and not balancing saving and spending.
Too often, he says some millennials seek instant gratification and buy items they want immediately on credit, instead of saving up for it first.
"Because you want something doesn't mean you can afford to buy it," Mr. Rivard says.
Another common mistake is not setting and sticking to a budget, an exhausted piece of advice that too few follow.
"If they built a budget it would relieve so much stress," says Mr. Rivard. "Doing a budget increases accountability and improves discipline."
Chris Enns, a Toronto-based financial planner who works with a lot of artists, actors and singers, says some of his clients don't believe at first that they can budget because their income is inconsistent.
"It's more difficult to budget, but it's possible, it just takes a bit of a different technique," Mr. Enns says.
Mr. Enns says a trap many millennials fall into is basing investment decisions on what they see or read about in advertising and on social and traditional media.
"The thing about information is that it doesn't necessarily apply to your life, or what you want," he says.
An example could be contributing to a registered retirement savings plan (RRSP), especially during the product push at this time of year, instead of figuring out if a tax-free savings account (TFSA) is better for them.
"The mistake is asking the wrong questions and obsessing about information that doesn't necessarily apply to your life or the things that you want," Mr. Enns says.
"It has to be goal first, process second and really finding what you want to drive your money questions – before anything else matters."
Too often, Mr. Enns says people avoid learning about investing because they don't understand it, or aren't proficient with money.
"That was my story as well. I avoided dealing with money for a long time because I assumed I would be bad at it," says Mr. Enns, who is also a freelance opera singer.
"The mistake people make is that they assume, because they aren't math inclined or they're not in love with spreadsheets, that they can't be good at dealing with their money," he says. "So much of money is about behaviour and so much of money is about more than just numbers and spreadsheets. That's what I realized and it was very empowering."
Ms. Fields says she has been working on her financial literacy ever since she made her mistakes with her credit card years ago. She hasn't taken a cash advance since, and pays her credit card bill every month, often well ahead of its due date.
"I monitor everything to the penny," she says of her saving and spending habits.
Her advice to others is to fully understand the charges that come with using a credit card.
"Learn about credit cards before you get into debt – and only spend what you already have in the bank," Ms. Fields says.
Today, she manages construction projects for a hospital in Winnipeg.
"Now I'm always working with budgets," she says.