Albert Einstein allegedly called compound interest "the eighth wonder of the world." While the quote may be apocryphal, the mathematics behind compounding is genuinely powerful and essential for every Canadian investor to understand.
What Is Compound Interest?
Compound interest is interest earned on both your original investment (principal) and on previously earned interest. Unlike simple interest, where you only earn returns on the principal, compounding allows your money to grow exponentially over time.
The Formula
A = P(1 + r/n)^(nt)
Where:
- A = Final amount
- P = Principal (initial investment)
- r = Annual interest rate
- n = Number of times interest compounds per year
- t = Number of years
Simple vs Compound Interest
Simple Interest Example
You invest $10,000 at 7% annually:
- Year 1: $10,000 + $700 = $10,700
- Year 2: $10,700 + $700 = $11,400
- Year 5: $13,500
Compound Interest Example
Same $10,000 at 7% compounded monthly:
- Year 1: $10,723
- Year 2: $11,505
- Year 5: $14,106
The difference compounds significantly over time.
Why Time Matters
The Power of Starting Early
Starting at age 25 vs age 35 with $500/month at 7%:
- Starting at 25: $1,022,504 by age 65
- Starting at 35: $504,373 by age 65
That 10-year difference results in over $500,000 more at retirement.
The Rule of 72
To estimate how long it takes your money to double, divide 72 by your annual return rate:
- At 7%: 72 ÷ 7 = ~10.3 years
- At 8%: 72 ÷ 8 = 9 years
- At 5%: 72 ÷ 5 = 14.4 years
Compound Interest in Canadian Accounts
Tax-Free Savings Account (TFSA)
Investment growth is tax-free, so compounding isn't reduced by annual taxes.
Registered Retirement Savings Plan (RRSP)
Growth compounds tax-deferred, but withdrawals are taxed as income.
Non-Registered Accounts
You're taxed annually on interest and dividends, which can significantly reduce the compounding effect unless held in tax-efficient investments.
Maximizing Compound Interest
Strategies for Canadians
- Start Early: Even small amounts benefit from time
- Maximize TFSA: Tax-free growth is powerful
- Reinvest Dividends: Dividend reinvestment plans (DRIPs) compound your returns
- Low-Fee Investments: Fees reduce your effective returns
- Automate Contributions: Regular investing ensures consistent compounding
The Impact of Fees
A 1% annual fee over 30 years can reduce a $500,000 portfolio by approximately $185,000.
Compound Interest in Debt
Compound interest works against you with debt:
- Credit card debt compounds daily
- The longer you carry a balance, the more interest accumulates
- Minimum payments barely cover interest, never reducing principal
The Snowball Effect (Negative)
$5,000 credit card balance at 19.99% with minimum payments:
- Takes 23 years to pay off
- Total interest paid: $6,500+
FAQ
Does compound interest apply to stocks?
When you reinvest dividends or see stock price appreciation on increasing stock value, your returns compound over time. This is one reason buy-and-hold investing is so powerful.
How often should I compound?
More frequent compounding (monthly vs annually) results in slightly higher returns, though the difference is usually minimal.
Is compound interest better than simple interest?
For investments, yes. For loans, no. Always seek simple interest for loans and compound interest for investments.