Compound Interest Calculator

Simulate your investment growth with taxes, inflation, monthly deposits and real return — free and professional.

How to use this calculator

1
Enter your capital
Set your initial investment, currency and expected annual return rate.
2
Configure deposits
Add monthly or yearly contributions with optional annual increase.
3
Add tax & inflation
See your real net return after tax and purchasing power adjustment.
4
Analyse & compare
Save a scenario and change variables to compare two strategies side by side.
Initial Investment
Deposits
Tax & Inflation
Summary
Final Gross Balance
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Total Interest
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Total Invested
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Net After Tax ?
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Inflation Adjusted ?
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Compounded Rate ?
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TWR Return ?
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Evolution Breakdown
Year Interest Accrued Interest Total Invested Balance

Compound Interest — FAQ

Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest (which grows linearly), compound interest grows exponentially. The longer your money stays invested, the more powerful the effect. Einstein famously called it the "eighth wonder of the world."
The standard formula is: A = P × (1 + r/n)n×t

A = final amount  |  P = principal  |  r = annual rate (decimal)  |  n = compounding periods/year  |  t = years.

Example: €5,000 at 9% compounded monthly for 15 years → ≈ €18,271.
The nominal rate is the basic percentage stated by financial institutions. The effective rate accounts for how often interest is compounded. A 10% nominal rate compounded monthly gives a 10.47% effective annual rate. This calculator shows the effective rate in the Summary panel.
Always, for long-term investing. Simple interest earns the same fixed amount each year. Compound interest earns interest on your interest, creating exponential growth. Over 20+ years, the gap between the two can be hundreds of thousands of euros on the same initial investment.
Divide 72 by your annual interest rate to quickly estimate how many years it takes to double your money.

6% → doubles in 12 years  |  9% → 8 years  |  12% → 6 years
More frequent compounding yields higher returns, but the gains diminish quickly. The difference between monthly and daily compounding at 9% is just ~0.04% per year — negligible. What truly matters is your rate of return and time in the market.
The tipping point occurs when your annual interest earned exceeds your annual contributions. At this stage your money works harder than you do. This calculator detects this moment automatically and highlights it in the insight panel.
It depends on the product. Savings accounts are typically taxed on interest each year. ETFs and individual stocks are usually only taxed when you sell, allowing the full amount to compound tax-free for years. Use the Tax Rate field to model both scenarios.
Inflation erodes purchasing power. If your investment grows at 5% but inflation runs at 3%, your real return is only ~2%. The "Inflation Adjusted" field in this calculator shows your future balance converted into today's money — your true wealth picture.
Compound interest calculator showing investment growth chart with principal, deposits and total balance over 15 years

The Wisdom of the Masters

"Compound interest is the eighth wonder of the world. He who understands it, earns it; he who doesn't, pays it."

— Albert Einstein

Einstein recognised the mathematical beauty of exponential growth. In finance, small consistent actions today create disproportionate results in the future. The curve starts slow — but once it turns upward, it becomes unstoppable.

Warren Buffett: The Oracle of Omaha

Warren Buffett built a multi-billion dollar fortune using three ingredients: Time, Discipline, and Quality.

Remarkably, over 95% of his wealth was earned after his 65th birthday. He started at age 11 and never interrupted the compounding process.

"My wealth has come from a combination of living in America, some lucky genes, and compound interest."

"The stock market is a device for transferring money from the impatient to the patient."

"Someone is sitting in the shade today because someone planted a tree a long time ago."

"Do not save what is left after spending, but spend what is left after saving."

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