What Is Compound Interest and Why It Matters in Your 20s

At some point in your 20s, someone probably told you that investing early is important and then explained compound interest with a vague phrase about “interest earning interest.” It sounds good, but it also sounds abstract - and abstract money advice is easy to ignore when you’re trying to cover rent, pay down student loans, and maybe still have a life. The thing is, compound interest is one of the few financial concepts that, once you see it illustrated with real numbers, changes how you think about money permanently. It’s not a motivational poster. It’s math. And the math says that the gap between starting at 22 versus starting at 32 is far larger than most people expect - not because of discipline or sacrifice, but because of how time interacts with growth. This is worth understanding before another year goes by.

How Compound Interest Actually Works

Interest is the return your money earns. Simple interest means you earn a return only on the original amount you invested - the principal. Compound interest means you earn a return on the principal plus all the returns you’ve already accumulated.

Here’s the difference. Say you invest $1,000 at a 7% annual return.

With simple interest: you earn $70 every year. After 30 years, you have $3,100 ($1,000 + $70 x 30).

With compound interest: in year one you earn $70, giving you $1,070. In year two you earn 7% on $1,070 - that’s $74.90, not $70. In year three you earn 7% on $1,144.90. The base keeps growing. After 30 years at 7% compounded annually, your original $1,000 becomes $7,612. Same investment, same rate, massively different outcome.

This is why the phrase “interest on interest” matters. The longer time goes on, the more the returns from previous years are themselves generating new returns. The growth isn’t linear - it curves upward.

The Real Numbers: What $100/Month Becomes

The example that tends to land hardest is a monthly contribution comparison.

If you invest $100 per month starting at 22, and your investments grow at an average of 7% per year (roughly the long-run average return of a broad Canadian and global equity index), by age 65 you’ll have approximately $298,000. Your total contributions over 43 years would be $51,600. The rest - about $246,000 - is compound growth.

If you wait until 32 to start the same $100/month, you’ll have about $143,000 by age 65. Same monthly amount, same return. But by starting 10 years later, you end up with roughly $155,000 less.

Now if you want to catch up from 32 and reach the same ~$298,000, you’d need to contribute about $210/month - more than double - to arrive at the same place.

This is the cost of waiting. Not a judgment, just math.

Quick tip: You don’t need a lot to start. Open a TFSA on Wealthsimple or Questrade, buy a single all-in-one ETF like XBAL or VGRO, and set up a $50 automatic monthly contribution. You can increase it later. The goal right now is to let time start working for you.

Why Your TFSA Is the Perfect Vehicle for This

For Canadians in their 20s, the TFSA is the ideal account to let compound interest work without tax drag. Every dollar of growth - dividends, capital gains, interest - accumulates tax-free inside the TFSA. When you withdraw the money in retirement, you pay no tax on any of it.

Compare this to a taxable investment account: every year, dividends are taxed as income, and when you sell you owe capital gains tax. Over 40 years, the difference in after-tax wealth is significant.

The 2026 TFSA limit is $7,000 for the year. If you’ve never contributed, your total accumulated room since 2009 (if you were 18 then) is $102,000. You don’t have to use all of it - the point is that you have space. Even $50–$100/month into a TFSA holding a diversified ETF puts you on the right side of the compound growth equation.

The RRSP works similarly for long-term tax-advantaged growth and adds an upfront tax deduction. Many young Canadians prioritize the TFSA first because contributions aren’t permanently lost when you withdraw - the room comes back the next January.

One More Thing: Compound Interest Goes Both Ways

Everything said above about compound growth also applies to compound debt. A credit card balance at 22% interest that you carry for years doesn’t just grow - it compounds. A $3,000 balance you don’t pay off for three years becomes roughly $5,500 in total cost. The same mechanism that makes long-term investing powerful makes long-term high-interest debt devastating.

This is why paying off credit card debt before investing is almost always the right call. No realistic investment return beats a guaranteed 22% by eliminating the debt.

Frequently Asked Questions

How does compound interest work in a Canadian TFSA?

Inside a TFSA, your investments grow tax-free - that includes any interest, dividends, and capital gains. Compound interest works the same way it does anywhere else: your returns accumulate on top of previous returns over time. The difference is that in a TFSA, CRA doesn’t take a cut of that growth each year the way it would in a taxable account, so more of your money stays invested and compounds. This makes the TFSA one of the most powerful long-term wealth-building tools available to Canadians.

What is a realistic rate of return for a young Canadian investor?

The long-run average annual return of a broad global equity index (like the MSCI World or the S&P 500) has historically been around 7–10% before inflation, depending on the time period. A balanced portfolio including bonds is lower - roughly 5–7%. These returns are not guaranteed and include years of significant losses, but they’re reasonable assumptions for long-term planning. Most compound interest calculators use 6–7% as a conservative estimate for a diversified equity portfolio.

What is the best investment account for compound growth in Canada?

The TFSA is usually the best starting point for young Canadians because growth and withdrawals are completely tax-free. The RRSP is also powerful for long-term growth, especially once you’re in a higher tax bracket and the upfront deduction becomes more valuable. For most people under 30, the priority order is: TFSA first, then RRSP, then taxable account. All three accounts can hold the same types of investments - the account is just the tax wrapper around them.

Is compound interest the same as compound growth in an ETF?

The mechanics are the same. When you hold an ETF in a TFSA and it grows by 7% in a year, your balance is larger. Next year’s 7% growth is applied to the larger balance - that’s compound growth. The term “compound interest” technically refers to interest-bearing instruments, but in practice it’s used broadly to describe this same reinvestment effect whether your returns come from interest, dividends, or capital appreciation. An all-in-one ETF like XEQT or VGRO benefits from compound growth in this sense.

How much do I need to start investing in Canada?

Almost nothing. Wealthsimple allows you to open a TFSA with no minimum deposit and buy fractional shares of ETFs with as little as $1. Questrade requires a $1,000 minimum to open an account but charges no commission on ETF purchases. The practical threshold for compound growth to work is just enough consistency to stay invested - $25/month is better than nothing, $100/month makes a meaningful difference over decades, and increasing contributions as your income grows accelerates it further.

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