Compound Interest Calculator
Calculate how your investments grow over time with compound interest. Add regular contributions and compare compounding frequencies to maximize your returns.
Final Balance
$49,268
Total Interest
$39,268
Total Contributions
$10,000
Effective Rate (APY)
8.300%
Growth Breakdown
📐 Rule of 72
At 8%, your money doubles approximately every 9.0 years.
Year-by-Year Breakdown
| Year | Start Balance | Interest | Contributions | End Balance |
|---|---|---|---|---|
| 1 | $10,000 | $830 | $0 | $10,830 |
| 2 | $10,830 | $899 | $0 | $11,729 |
| 3 | $11,729 | $973 | $0 | $12,702 |
| 4 | $12,702 | $1,054 | $0 | $13,757 |
| 5 | $13,757 | $1,142 | $0 | $14,898 |
| Total | — | $39,268 | $10,000 | $49,268 |
⏳ The Power of Starting Early
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What is Compound Interest?
Compound interest is often called the "eighth wonder of the world." It's interest calculated on both the initial principal and all previously accumulated interest — creating an accelerating growth effect over time.
Unlike simple interest (which only earns on the original amount), compound interest means your money earns money, and then that money earns even more money. The longer you invest, the more dramatic the effect becomes.
Compound Interest Formula
A = P(1 + r/n)nt
Where: A = final amount, P = principal (initial investment), r = annual interest rate (decimal), n = compounds per year, t = time in years.
Example: $10,000 at 8% compounded monthly for 20 years: A = 10,000 × (1 + 0.08/12)12×20 = $49,268.03. That's $39,268 in interest without adding a single dollar!
The Power of Starting Early
Investing $200/month starting at age 25 at 10% returns gives you about $1.26 million by age 65. Wait until 35 and you get $456,000. Wait until 45 and only $153,000.
The person who starts at 25 invests only $24,000 more than the person who starts at 35, but ends up with $800,000+ more. Time is the most powerful factor in compound growth.
Investment Strategies
• Dollar-cost averaging: Invest a fixed amount regularly regardless of market conditions. This reduces the impact of volatility.
• Rate vs principal: A higher interest rate has a larger long-term impact than a larger initial investment, especially over decades.
• Compounding frequency: Daily vs monthly makes a small difference, but any compounding frequency is dramatically better than simple interest.
• Reinvest dividends: Always reinvest earnings for maximum compound growth. Taking dividends out breaks the compounding chain.
Compound Interest Examples
| Scenario | Initial | Monthly | Rate | Years | Result |
|---|---|---|---|---|---|
| Retirement | $10K | $500 | 10% | 40 | $3.16M |
| College Fund | $5K | $300 | 7% | 18 | $131K |
| Emergency | $1K | $200 | 5% | 5 | $14.7K |
| Down Payment | $20K | $800 | 6% | 7 | $97K |
| Wealth Building | $50K | $1,000 | 8% | 25 | $1.07M |