Compound Interest Calculator
See exactly how your money grows over time. Enter your principal, rate, and time period — get a full year-by-year breakdown instantly.
| Year | Total deposited | Interest earned | Balance |
|---|---|---|---|
| Year 1 | $12,400 | $920 | $13,320 |
| Year 2 | $14,800 | $2,116 | $16,916 |
| Year 3 | $17,200 | $3,609 | $20,809 |
| Year 4 | $19,600 | $5,427 | $25,027 |
| Year 5 | $22,000 | $7,594 | $29,594 |
| Year 6 | $24,400 | $10,140 | $34,540 |
| Year 7 | $26,800 | $13,097 | $39,897 |
| Year 8 | $29,200 | $16,498 | $45,698 |
| Year 9 | $31,600 | $20,381 | $51,981 |
| Year 10 | $34,000 | $24,786 | $58,786 |
| Year 11 | $36,400 | $29,755 | $66,155 |
| Year 12 | $38,800 | $35,336 | $74,136 |
| Year 13 | $41,200 | $41,579 | $82,779 |
| Year 14 | $43,600 | $48,539 | $92,139 |
| Year 15 | $46,000 | $56,277 | $102,277 |
| Year 16 | $48,400 | $64,856 | $113,256 |
| Year 17 | $50,800 | $74,346 | $125,146 |
| Year 18 | $53,200 | $84,823 | $138,023 |
| Year 19 | $55,600 | $96,369 | $151,969 |
| Year 20 | $58,000 | $109,072 | $167,072 |
What is Compound Interest?
Compound interest is interest earned on both your initial investment (principal) and the interest already accumulated. It's often called "interest on interest" and represents one of the most powerful concepts in personal finance. Unlike simple interest, which only earns returns on your principal, compound interest creates exponential growth. This means your money grows faster over time—the longer you invest, the more dramatic the compounding effect becomes. Albert Einstein allegedly called it "the eighth wonder of the world." That's because compound interest works silently in the background, multiplying your wealth exponentially if you give it enough time. For example, if you invest $10,000 at 8% annual interest with annual compounding, after 10 years you'll have $21,589. But if you invested the same amount at the same rate with monthly compounding (more frequent), you'd have $22,196—an extra $607 with no additional effort. The difference grows even larger over longer periods. HOW DOES COMPOUND INTEREST WORK? Every time interest is calculated and added to your account, that new total becomes the base for the next interest calculation. This creates a snowball effect: Year 1: You earn interest on your initial principal Year 2: You earn interest on (principal + year 1 interest) Year 3: You earn interest on (principal + year 1 + year 2 interest) ...and so on. The more frequently interest compounds, the faster your money grows. A savings account might compound daily, while a CD might compound annually. A stock portfolio compounds whenever you reinvest dividends. THE POWER OF TIME Compound interest is dramatically more powerful the longer you invest. Here's why: early contributions have decades to compound, while later ones have less time. If you invest $100/month starting at age 25, that money compounds for 40 years. Someone starting at 45 gets only 20 years of compounding—less than half the time, but exponentially less growth. This is why starting early, even with small amounts, beats starting late with large amounts. A 25-year-old investing $100/month at 8% will have significantly more at age 65 than a 45-year-old investing $500/month at the same rate, despite putting in less total money. PRACTICAL APPLICATIONS Compound interest works in your favor when you're saving or investing. It works against you when you're borrowing (credit card debt, loans). Understanding which side of the equation you're on is critical to building wealth. Common scenarios where compound interest matters: • Savings accounts and CDs (works for you) • Investment portfolios and index funds (works for you, especially with reinvested dividends) • Retirement accounts like 401(k)s and IRAs (works powerfully for you over decades) • Credit card debt (works against you—dangerous compound interest) • Mortgages (works against you, though the interest is tax-deductible in some cases) • Student loans (works against you while in school if interest is accruing)
The Compound Interest Formula
In this formula: • A = The final amount you'll have • P = Your principal (starting amount) • r = The annual interest rate (as a decimal, so 8% = 0.08) • n = Number of times interest compounds per year (annually=1, quarterly=4, monthly=12, daily=365) • t = Number of years For example, if you invest $10,000 (P) at 8% annual interest (r=0.08) compounded monthly (n=12) for 10 years (t=10), you'd substitute these values into the formula to get your final amount.
Worked Examples
Example 1: Tax-Free Savings Account (TFSA) Growth
Scenario: You invest $10,000 in a high-interest savings account with 5% annual interest, compounded daily, for 20 years. Using the formula with daily compounding: A = $10,000 × (1 + 0.05/365)^(365×20) = $10,000 × (1 + 0.000137)^7,300 = $10,000 × 2.7183 = $27,183 After 20 years, your initial $10,000 becomes $27,183. That's $17,183 in pure interest—a 172% return on your original investment. Notice that daily compounding generates slightly more than monthly or annual compounding would. The real power: If you never touched this money and let it sit for 30 years instead, it would grow to $48,662. That extra 10 years nearly doubles your return again. This is why long-term investing is critical.
Example 2: Building a 6-Month Emergency Fund with Monthly Contributions
Scenario: You start with $2,000 and contribute $300 every month to a high-yield savings account earning 4.5% annual interest, compounded monthly. After 24 months, you want to see how much you've accumulated. Total principal contributed: $2,000 + ($300 × 24) = $9,200 Interest earned through compounding: Approximately $680 Final balance: About $9,880 This shows why automatic, consistent contributions are powerful. Your $300 monthly habit grows faster than if you just had $7,200 sitting idle—compound interest adds that extra $680. And because it's automated, you're less likely to touch the money. Real-world application: This is exactly how an emergency fund works in practice. Start small, automate your contributions, and let compounding fill in the gaps over time.
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Use it →Frequently asked questions
Everything you need to know about compound interest calculations.
What is compound interest?
Compound interest is interest calculated on both the initial principal and the accumulated interest. Unlike simple interest (which is only on the principal), compound interest grows exponentially over time.
Which compounding frequency is best?
More frequent compounding (daily vs. annually) yields slightly more interest. However, the difference is small — the interest rate itself has far more impact on final results than compounding frequency.
Does this account for inflation?
No — this calculator shows nominal (not inflation-adjusted) growth. To estimate real returns, subtract the inflation rate (typically 2–3%) from your interest rate before entering it.
How accurate is this calculator?
Very accurate for standard compound interest. It uses the exact compound interest formula with monthly contributions added at each compounding interval. Results may differ slightly from bank statements due to rounding.
What's the difference between annual and monthly compounding?
Annual compounding calculates interest once a year. Monthly compounding calculates it 12 times per year, and each calculation includes previously earned interest. Daily compounding does this 365 times. More frequent compounding = slightly more interest, but the effect is usually small compared to the interest rate itself.
Why isn't my bank balance matching the calculator?
Common reasons: Your bank may compound on a different schedule than you selected, fees reduce your balance, or the rate isn't fixed (it changed during the period). Also, banks often round to the nearest cent, which can create small discrepancies over time. This calculator assumes consistent interest rates and no fees.
What's a common mistake people make with compound interest?
Underestimating how powerful time is. Many people think starting late with larger amounts beats starting early with smaller amounts—it doesn't. A 25-year-old investing $100/month beats a 45-year-old investing $500/month. Also, people often don't account for how quickly debt compounds against them (credit cards, loans).
Can I use this to calculate investment returns?
Yes, if your investment has a consistent annual return rate. However, stocks and mutual funds don't have guaranteed returns—they fluctuate. Use this calculator to see potential returns under a given scenario, but understand that actual results will vary. For conservative planning, use a lower rate than historical averages.
How do I account for taxes on my earnings?
This calculator shows pre-tax results. To estimate after-tax returns, multiply the interest earned by (1 - your tax rate). For example, if you earned $1,000 in interest and your tax rate is 24%, you'd keep about $760. Tax-advantaged accounts (401k, Roth IRA) don't require this adjustment during accumulation.