Wealth growth calculator

How wealth builds over time

Starting capital, regular contributions, an assumed return, and time determine this projection. The calculator compounds the balance each month. You do not need an ETF, a brokerage account, or data stored with Investboard to use it.

Three inputs carry most of the result: the monthly contribution, the length of the plan and the assumed return. A fourth, the annual increase of the contribution, matters more than it first appears, because every later contribution starts from a higher level.

Historical US equity reference · NYU Stern: 10th, 50th and 90th percentiles of 79 overlapping 20-year annualized total-return windows, 1928–2025. USD, dividends reinvested; predecessor US stock history before 1957. These are past observations, not future probabilities.

How the calculator works

The calculator adds your contribution at the start of each month and lets the whole balance grow at the assumed return, month by month. An initial investment, if you enter one, compounds from the first month. Once a year the monthly contribution rises by the increase you choose.

The result shows the final value, the sum of your contributions, the growth on top of them and the path year by year.

Choose the amounts in your own money with Currency. The math is the same in every currency: the calculator converts nothing, it applies the same compounding to whatever amounts you enter.

What the calculator simplifies

Historical mode uses horizon-matched 10th, 50th and 90th percentiles of annualized US equity total returns compiled by NYU Stern for 1928–2025. Custom mode lets you enter all three annualized rates. Neither mode predicts future returns. Three smooth paths use constant effective annual returns, converted to monthly rates as (1 + r)^(1/12) − 1. Contributions enter at the beginning of each month. Historical references or your own assumptions are not forecasts. The same reference rates are applied to your chosen currency. Exchange-rate changes are not modeled.

Fund costs are not included. Ongoing charges, tracking difference, spreads and order costs reduce the return on top of this; how they work is explained in ETF costs: understanding TER and tracking difference. A practical approach is to subtract the expected cost ratio from your return assumption.

Inflation is not deducted either. The final value is a nominal amount, so it buys less than the same figure would today.

By default the result is before tax. Most tax systems tax investment gains at some point, often when you sell. The calculator deducts no tax at the end of the term in any mode: the final value is calculated before you sell.

If you are taxed in Germany

German investors in accumulating funds pay an annual advance tax, the Vorabpauschale, even while they sell nothing. It lowers the capital that keeps compounding. The calculator can model this drag as an option. Because German tax is calculated in euros, the switch appears only when Currency is set to EUR.

With the option on, the calculator computes the Vorabpauschale on the value at the start of each modeled year and deducts the tax due from the portfolio at year end. Contributions made during the same year do not increase it: they are removed from the year's gain before the statutory cap applies, because fresh savings are not income.

The tax rate is the familiar stack of 25% capital income tax plus the 5.5% solidarity surcharge on it, and, if you pay church tax, 8% or 9% church tax depending on the federal state.

Before that rate applies, the partial exemption (Teilfreistellung) for the fund type removes a share of the Vorabpauschale, and the saver's allowance (Sparerpauschbetrag) covers the rest up to its limit: EUR 1,000 for single filers, EUR 2,000 for jointly assessed couples, granted afresh in every modeled year.

Yes. The calculator grants the full Sparerpauschbetrag in every modeled year: EUR 1,000 for single filers, EUR 2,000 for jointly assessed couples. It often covers the advance tax in the early years; when tax starts depends on your inputs and the return scenario.

The calculator applies one base rate (Basiszins) to every year: 3.20%, the figure for 2026. That is a deliberate simplification, not a forecast: the base rate is set anew each year and cannot be stated for future years. The step-by-step derivation is in the Vorabpauschale calculator.