How is compound interest calculated?

Future value is principal times (1 + rate) raised to the number of compounding periods. Each monthly contribution is grown from the month it is added, and you can choose beginning-of-period or end-of-period contribution timing.

How are fees modeled?

Fees (expense ratios) are deducted from the portfolio balance each month rather than subtracted from the return rate, which accurately models how real fund fees work — the same fee rate costs more in absolute terms on a larger portfolio.

What is the difference between nominal and real value?

Nominal value is the future account balance in future currency. Real value divides the nominal value by inflation, showing what that balance is worth in today's purchasing power.

What does the Monte Carlo simulation do?

Instead of a single constant return, the Monte Carlo simulation randomizes each year's return from a normal distribution centered on your expected return with your specified variance, then runs 1,000+ trials to show percentile bands (P10–P90) of likely outcomes.

Can it model a retirement withdrawal phase?

Yes. The decumulation phase simulates regular monthly withdrawals from the accumulated portfolio with ongoing returns, fees and optional inflation adjustments, and solves for the maximum sustainable and capital-preserving (perpetual) withdrawal rates.

Compound Investment Calculator — Inflation, Tax & Monte Carlo

Parameters

Global Settings

Scenario Name

Currency

Compounding Frequency

Contribution Timing

Annual Return

Return must be between 0 and 100%

Interest Rate Variance (±)

Annual Inflation

Inflation must be between 0 and 50%

Annual Fees / Expense Ratio

Fees must be between 0 and 10%

Note: For non-monthly compounding, contributions are still added monthly but compound at the selected interval.

Overlay standard benchmarks

Net Annual Rate (Return − Fees)

9.77%

Tax Settings

Tax Treatment

Income Context (optional)

Monthly Net Income

€

Savings Rate

Withdrawal Phase (decumulation)

Simulate withdrawal phase

Time Horizons

Investor Profiles

Color	Name	Initial	Monthly	Growth	Actions

Add at least one investor profile and fill in return, inflation, fee, and variance to enable calculation.

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Ready for Simulation

Please fill in the return rate, inflation, fee, and volatility settings in the parameters panel and click Calculate to view results.