💹 Compound Interest Calculator
Calculate daily, monthly, quarterly & annual compounding in 30+ currencies. See year-by-year growth, export results, and discover how your money multiplies.
↺ Reset
Fill in your investment details on the left and press Calculate to see your compound interest growth chart and year-by-year breakdown.
Zero Data Storage — Your financial data never leaves your device
Every calculation runs entirely in your browser using JavaScript. No principal amounts, interest rates, or personal data are ever transmitted to any server, stored in any database, logged or tracked. See our Zero Data Storage Policy for full details.
What Is Compound Interest? The Complete Guide
Compound interest is the process of earning interest on both your original principal and on the interest you've already accumulated. Often described as "interest on interest," it creates exponential growth over time — making it one of the most powerful forces in personal finance and investing.
Albert Einstein reportedly called compound interest "the eighth wonder of the world," saying: "He who understands it, earns it; he who doesn't, pays it." Whether this quote is historically accurate or not, its wisdom is undeniable — compound interest can work powerfully for you in savings and investments, or powerfully against you in debt.
A — Final Amount
The total value of your investment after t years, including all compounded interest and contributions.
P — Principal
Your initial investment or deposit — the starting amount before any interest is applied.
r — Annual Rate
The annual interest rate expressed as a decimal. 7% becomes 0.07 in the formula.
n — Compounding Periods
How many times per year interest compounds. Monthly = 12, Daily = 365, Annually = 1.
t — Time (years)
The total duration of the investment. Longer periods produce dramatically larger results due to exponential growth.
Compounding Frequency: Daily vs Monthly vs Annual
More frequent compounding means you earn interest on your interest more often, resulting in a slightly higher final balance. Here's a concrete comparison starting with $10,000 at 7% for 20 years:
| Compounding Frequency | Times/Year (n) | Final Balance | Total Interest | Effective APY |
|---|---|---|---|---|
| Annually | 1 | $38,697 | $28,697 | 7.000% |
| Semi-annually | 2 | $39,316 | $29,316 | 7.123% |
| Quarterly | 4 | $39,638 | $29,638 | 7.186% |
| Monthly | 12 | $40,022 | $30,022 | 7.229% |
| Daily | 365 | $40,139 | $30,139 | 7.250% |
The Rule of 72: How Long to Double Your Money?
The Rule of 72 is a simple mental shortcut: divide 72 by your annual interest rate to find roughly how many years it takes to double your investment. At 6%, your money doubles in 72 ÷ 6 = 12 years. At 9%, it doubles in just 8 years.
At 4% (savings account)
Doubles in ~18 years. Safe but slow — suitable for short-term goals.
At 7% (index fund)
Doubles in ~10.3 years. Historical average for diversified stock market investing.
At 10% (aggressive)
Doubles in ~7.2 years. Higher potential, higher volatility. S&P 500 historical average.
At 12% (high growth)
Doubles in ~6 years. Requires higher-risk investments. Always account for volatility.
Compound Interest vs Simple Interest
With simple interest, you only ever earn interest on the original principal: I = P × r × t. With compound interest, each period's interest is added to the principal, and the next period's interest is calculated on the new, larger balance. The difference becomes dramatic over decades.
Example: $5,000 at 8% for 30 years — Simple interest yields $17,000. Compound interest (monthly) yields $54,982 — more than 3× as much.
How to Maximise Your Compound Interest
Start as early as possible
Every decade of delay roughly halves the benefit of compounding. Starting at 25 vs 35 can mean hundreds of thousands in retirement.
Make regular contributions
Adding even modest monthly amounts dramatically accelerates growth. Our calculator shows the exact impact of contributions.
Reinvest all returns
Never withdraw interest early. Compounding only works when interest is reinvested. Use dividend-reinvestment plans (DRIPs) for stocks.
Choose higher-frequency compounding
When comparing savings accounts, choose daily or monthly compounding over annual. Check APY — not just APR — for accurate comparison.