Compound Interest

The rate you enter is nominal annual: it is divided by 100 and by 12 to obtain the monthly rate. Each month, that rate is applied to the accumulated balance. Without contributions, 8% nominal yields approximately 8.30% effective annually: (1 + 0.08 / 12)^12 - 1.

Contributions are added at the end of each month, after interest is applied, and start earning interest the following month: new balance = previous balance × (1 + monthly rate) + monthly contribution.

For each year of each variable path, a new variation is chosen relative to the nominal rate you entered, not the previous year's rate. Its magnitude is uniform between 2 (inclusive) and 6 (exclusive) percentage points, with an equal chance of adding or subtracting. The resulting annual rate, which can be negative, is divided by 100 and by 12 and held for all 12 months of that year.

The variable path and the six additional lines are random examples. They do not come from a calibrated financial model and do not represent a probability range, a confidence interval or a market forecast.

Total invested is the initial capital plus all contributions. The interest and multiplier statistics refer only to the fixed rate: final balance minus total invested, and final balance divided by total invested, respectively. If total invested is zero, the displayed multiplier is ×1.00.

All amounts are in euros (EUR). Taxes, fees and inflation are not included. This calculator is for educational use, is not financial advice and does not guarantee outcomes or returns.