Investment Growth Simulator

Why Simulate Different Interest Rates, Contributions and Withdrawals?

Investment conditions change over time — different asset types yield different returns, and your contribution capacity might vary. By simulating multiple scenarios, you gain a more realistic understanding of long-term outcomes, especially when shifting your investment strategy near retirement or continuing to earn interest during withdrawal phases.

A single projection is a guess with a decimal point. Running the same horizon at two percentage points lower, or with the contribution stopping five years early, tells you something a single number cannot: how much of the result depends on assumptions you cannot verify. That is the question worth answering before committing money for thirty years.

A Realistic Investment Journey: Contributions, Shifts and Withdrawals

Imagine starting with 10,000 € and contributing 200 € per month for the first 5 years, then 400 € for the next 5, and finally 600 € for the following 10 years. During the first 15 years, you invest in higher-risk stocks with an assumed average return of 7 %. After that, you shift to more secure bonds with an assumed yield of 4 % for 5 years. Once you begin withdrawing, your money remains in a savings account with an assumed 3 % annually. This example shows how changing contribution levels and risk profiles can shape long-term growth — and how compounding continues even during withdrawal.

Every element of that example is a field in the calculator, and the resulting address is shareable. Change one input, copy the link, and you have a second scenario you can put next to the first — which is usually more informative than refining a single one.

What Is My Investment Horizon?

Your investment horizon doesn’t end when you start withdrawing funds. It's the entire period your money stays invested — before and after retirement. Simulating beyond the withdrawal start point helps you plan sustainably for the long term and estimate how long your capital might last.

Shortening the horizon pulls every contribution and withdrawal period in with it, so nothing is left pointing past the end of the simulation. That matters when you compare a plan for twenty years against the same plan for thirty: only the horizon changes, everything else stays where you put it.

Understanding Investment Contributions

Regular contributions — whether monthly, quarterly, or annually — are key to building wealth steadily. Even small recurring amounts can grow substantially when combined with compound interest. Automating your contributions helps maintain discipline and reduce emotional decision-making.

The relationship is strictly linear: doubling the monthly amount doubles the contributions, the interest and the final balance. The horizon is not linear, which is why moving the start date earlier beats raising the amount. You can model a rising contribution as up to three separate periods.

Annual vs. Monthly Contributions: Does Timing Matter?

Whether you pay in monthly or once a year changes the result less than most people expect. In the calculator the interest interval sets the sub-periods of the year and contributions are spread across them: with annual compounding a year's instalments count as paid in at the start of the year, with monthly compounding they are spread over the months. 300 € a month for twenty-five years at 6 % yields 118,938 € of interest compounded monthly and 119,363 € compounded annually — a gap under half a percent. On a real account the bank's value-dating decides from which day a deposit earns interest.

Put a number on it before you optimise: at 6 % over twenty years, switching a lump sum from annual to monthly compounding adds about 3 % to the final balance. One extra year at the same rate adds roughly twice as much. Frequency is worth understanding so nobody can use it to make a weaker product look stronger.

Withdrawals Don’t Stop Compounding

Even while taking money out, the remaining capital can continue to grow through compounding. Understanding this balance is key to making sustainable withdrawals without prematurely depleting your assets. Strategic planning allows you to withdraw while still benefiting from growth.

The sensitivity is sharp in this direction. On a portfolio of 500,000 € at 5 %, taking 2,500 € a month leaves money after thirty years; taking 3,000 € empties it in year 23. Twenty percent more income costs seven years of the plan, which is why a withdrawal rate deserves a stress test at a lower return.

Balancing Risk and Reward

Higher returns often come with higher risk. While it's tempting to aim for aggressive growth, balancing your risk tolerance with your financial goals is crucial. Diversification, time horizon, and consistency are more reliable than chasing quick gains.

Inflation belongs in the same trade-off. Six percent nominal with two percent inflation is 3.92 percent real, not four, and after half a percent of annual costs roughly 3.4 percent is left. Entering the real rate keeps every figure in the result in today's purchasing power, which is the only form comparable to a price you know.