Three numbers, one machine
Type what you start with, what you add every month, and how long you leave it. The machine shows two things: the money you paid in, and the money the interest added.
Example numbers with one fixed rate every year. Real returns move up and down and can be negative. This is maths practice, not advice.
Try these, then compare in the chat
- 1 · €25 a month at 5% — run it for 10, 20 and 40 years. When does the turquoise part get bigger than the grey part?
- 2 · Keep everything and change only the rate: 3%, 5%, 8%. How much does the rate change the end result?
- 3 · Two ways to reach a big number: double the monthly amount, or add 10 years. Which one helps more?
🤔 Before you test challenge 3 — what do you expect: more money per month, or more time?
Show answer
Over long periods, time usually wins — because every extra year works on a bigger amount. Doubling the monthly amount only doubles what you pay in. Test it with your own numbers and see where the line is.
✍️ Post one result in the chat: "€… a month for … years becomes €… — and €… of that is interest."
One sentence to keep
💡 The machine has three levers — amount, rate and time. Time is the strongest one, and it is the only one you cannot get back later.