Compound Interest Calculator
See how your money grows over time with compound interest and regular contributions.
Growth Over Time
Year-by-Year Breakdown
| Year | Contributions | Interest | Balance |
|---|---|---|---|
| 1 | $12,400.00 | $801.42 | $13,201.42 |
| 2 | $14,800.00 | $1,834.27 | $16,634.27 |
| 3 | $17,200.00 | $3,115.28 | $20,315.28 |
| 4 | $19,600.00 | $4,662.39 | $24,262.39 |
| 5 | $22,000.00 | $6,494.83 | $28,494.83 |
| 6 | $24,400.00 | $8,633.24 | $33,033.24 |
| 7 | $26,800.00 | $11,099.74 | $37,899.74 |
| 8 | $29,200.00 | $13,918.03 | $43,118.03 |
| 9 | $31,600.00 | $17,113.55 | $48,713.55 |
| 10 | $34,000.00 | $20,713.58 | $54,713.58 |
| 11 | $36,400.00 | $24,747.34 | $61,147.34 |
| 12 | $38,800.00 | $29,246.20 | $68,046.20 |
| 13 | $41,200.00 | $34,243.79 | $75,443.79 |
| 14 | $43,600.00 | $39,776.14 | $83,376.14 |
| 15 | $46,000.00 | $45,881.93 | $91,881.93 |
| 16 | $48,400.00 | $52,602.60 | $101,002.60 |
| 17 | $50,800.00 | $59,982.60 | $110,782.60 |
| 18 | $53,200.00 | $68,069.60 | $121,269.60 |
| 19 | $55,600.00 | $76,914.70 | $132,514.70 |
| 20 | $58,000.00 | $86,572.72 | $144,572.72 |
How to use
- 1
Enter your initial investment, annual interest rate, and time period using the sliders or input fields.
- 2
Add a monthly contribution amount to see how regular saving accelerates growth.
- 3
Choose your compounding frequency — monthly or daily compounding yields the most interest.
Compound Interest Calculator — Free Online, With Monthly Contributions
Calculate compound interest with initial investment, annual rate, compounding frequency, and monthly contributions. See year-by-year growth chart and breakdown table. Free, instant, no signup.
Compound interest is the process of earning interest on both your initial principal and the accumulated interest from previous periods. Albert Einstein reportedly called it the 'eighth wonder of the world' — and the numbers bear this out. A $10,000 investment at 7% annual return doubles in just over 10 years, quadruples in 20, and grows to nearly 15x in 40 years. Skycally's compound interest calculator shows you this growth year by year, including the effect of regular monthly contributions.
The compound interest formula is A = P(1 + r/n)^(n×t), where P is the principal, r is the annual interest rate as a decimal, n is the number of times interest compounds per year, and t is the time in years. Compounding frequency matters: daily compounding produces slightly more interest than monthly, which produces more than annual. For a $10,000 investment at 5% over 20 years, daily compounding yields about $27 more than monthly compounding — the difference is small but grows with larger principals and longer time periods.
The most powerful lever in the calculator is the monthly contribution. Adding even $200 per month to a $10,000 initial investment at 7% over 20 years grows the balance from $38,697 (no contributions) to $143,253 — nearly 4x more. This demonstrates why consistent, regular investing outperforms waiting to invest a large lump sum. The year-by-year table and chart make this growth curve easy to visualize and understand.
This calculator is useful for planning retirement savings, education funds, investment portfolios, savings accounts, and any scenario where money grows over time. The results are mathematical projections — actual investment returns vary and are not guaranteed. Always consult a qualified financial advisor before making investment decisions.
Frequently Asked Questions
What is the compound interest formula?
A = P(1 + r/n)^(n×t), where A is the final amount, P is the principal, r is the annual interest rate (as a decimal), n is the compounding frequency per year, and t is the time in years. For monthly contributions, the future value of an annuity formula is added: FV = C × [((1 + r/n)^(n×t) − 1) / (r/n)], where C is the periodic contribution.
What is the difference between simple and compound interest?
Simple interest is calculated only on the principal: Interest = P × r × t. Compound interest is calculated on the principal plus all previously earned interest, causing exponential growth. On a $10,000 investment at 5% over 10 years, simple interest yields $5,000. Compound interest (annually) yields $6,289 — 26% more.
Does compounding frequency matter?
Yes, but less than most people think. The difference between annual and monthly compounding is meaningful; the difference between monthly and daily is very small. For a $10,000 investment at 5% over 20 years: annual compounding → $26,533; monthly → $27,126; daily → $27,181. The bigger factor is always the interest rate and time period.
What is the Rule of 72?
The Rule of 72 is a quick mental shortcut: divide 72 by the annual interest rate to estimate how many years it takes to double your money. At 6%, it takes roughly 72 ÷ 6 = 12 years to double. At 8%, it takes 9 years. At 4%, it takes 18 years. This calculator shows the exact figure.
How much do monthly contributions affect the result?
Dramatically. A $10,000 investment at 7% for 20 years grows to about $38,700. Adding $200/month grows it to about $143,000. Adding $500/month grows it to about $260,000. Regular contributions are often more impactful than the initial lump sum, especially over long periods.
What annual return should I use?
Historical averages: S&P 500 index funds have returned approximately 7–10% annually before inflation (4–7% after inflation) over the long term. High-yield savings accounts currently offer 4–5%. Bonds average 2–4%. CDs average 3–5%. For conservative projections, use 5–6%; for stock-market scenarios, 7–8% is commonly used.
Is compound interest calculated on contributions too?
Yes. Each monthly contribution you make starts earning compound interest from the moment it's deposited. Earlier contributions benefit from more compounding periods than later ones. This is why financial advisors emphasize starting early — the first contributions you make compound the longest.
Is my data stored anywhere?
No. All calculations run instantly in your browser using JavaScript. Your investment figures are never transmitted to any server.
You might also like
Other tools you might find useful.