Compound Interest: Why Starting to Invest Early Can Matter
Starting early can make a difference to long-term investing because of compound growth: returns may themselves earn returns in later periods. The longer money remains invested, the more time compounding has to work—but actual results depend on investment returns and risk.
Educational example only: This hypothetical scenario is not a forecast or investment recommendation. It assumes a fixed 12% annual return and excludes inflation, taxes, fees, market volatility, and differences between financial products. A 12% return is not guaranteed.
The comparison below considers two people who contribute the same amount each year but start at different ages. It illustrates the effect of time; it does not predict the balance of a real investment account.
Two hypothetical retirement investing scenarios
João and Mário are friends who are both 19 and are thinking about retirement.
João invests R$2,000 per year from age 19 through 26: eight annual contributions totaling R$16,000. He then makes no additional contributions and leaves the balance invested until age 65.
Mário starts at age 27 and invests R$2,000 per year through age 65. In this scenario, that is 39 annual contributions totaling R$78,000.
Which person would have the larger balance at age 65 under these assumptions?
Assuming each contribution is made at the beginning of the year and earns 12% annually, the illustrative balances are:
| Age | João contributes | Mário contributes | João’s balance | Mário’s balance |
|---|---|---|---|---|
| 19 | R$2,000.00 | R$0.00 | R$2,240.00 | R$0.00 |
| 20 | R$2,000.00 | R$0.00 | R$4,748.80 | R$0.00 |
| … | … | … | … | … |
| 26 | R$2,000.00 | R$0.00 | R$27,551.31 | R$0.00 |
| 27 | R$0.00 | R$2,000.00 | R$30,857.47 | R$2,240.00 |
| 28 | R$0.00 | R$2,000.00 | R$34,560.37 | R$4,748.80 |
| … | … | … | … | … |
| 64 | R$0.00 | R$2,000.00 | R$2,043,747.11 | R$1,366,020.39 |
| 65 | R$0.00 | R$2,000.00 | R$2,288,996.76 | R$1,532,182.84 |
Under this simplified model, João ends with a larger balance even though he contributes for fewer years. His first contributions have more time to grow. The example also separates total contributions from time invested: João contributes R$16,000, while Mário contributes R$78,000.
These figures assume contributions at the start of each year and annual compounding at 12%; changing the timing changes the result. Inflation is excluded, so future balances do not represent today’s purchasing power. In reality, returns vary and can be negative. Neither the strategy nor the figures are guaranteed to produce the same outcome.
Explore the assumptions
You can change the contributions and hypothetical return in the simulation spreadsheet to see how different assumptions affect the result.
This article is part of my personal financial education journey. If you have a question about the example, get in touch.