Invest more now, or increase your contributions over time?
Two plans can invest exactly the same money and end tens of thousands apart — only because of when the money arrives. This guide walks through the arithmetic, with a calculator so you can test your own numbers. It explains; it does not advise.
Notice: This is a calculation tool, not financial advice. The results are estimates: they assume a constant rate that you choose yourself and leave out taxes, fees, currency exchange and real market risk. No return is guaranteed — investment decisions are your own responsibility.
Why timing matters
Compound interest is paid on everything already in the account — including past interest. So each franc works for as long as it stays invested: in a ten-year plan, a franc contributed in the first month compounds for 120 months; one contributed in the final year, for about twelve.
That is the whole mechanism. For a fixed assumed rate, whether contributions land early or late is not a matter of opinion — it is arithmetic.
Two plans, the same 180'000
Compare two ten-year plans that invest exactly the same money — 180'000 in total — under the same assumptions: a constant 5% effective annual return (an assumption you pick yourself, not a forecast), contributions at the start of each month, and no taxes, fees or inflation in the picture.
- Plan A — more at the start: 2'000 per month for five years, then 1'000 per month for five years.
- Plan B — increase later: 1'000 per month for five years, then 2'000 per month for five years.
| Invested | Interest | Final balance | |
|---|---|---|---|
| Plan A (2'000 → 1'000) | 180'000 | 61'894 | 241'894 |
| Plan B (1'000 → 2'000) | 180'000 | 43'082 | 223'082 |
Same money in, but plan A ends 18'812 higher — about 8.4% more — because the larger contributions arrived early enough to keep compounding through the entire second half of the plan.
Check it yourself
Both plans open in the phases calculator as two separate tabs, so you can switch between them: the timeline shows each plan's phases, and the table shows every single month. Change any number and watch the gap move.
What the arithmetic leaves out
Numbers this clean hide everything that makes real plans personal. Most incomes rise over the years, so many people simply cannot start high. A contribution too ambitious to sustain can end worse than a modest one kept up for the whole period. Returns are not constant in reality — 5% here is a chosen assumption, and actual markets spend years far above and far below it. And taxes, fees and inflation all take their share.
This page shows how the mechanics behave; it does not — and cannot — say which plan fits any particular person's situation.
About this guide. This is educational content about the mathematics of compound interest. Alpine Lynx is not a licensed financial adviser and does not provide investment advice or recommendations. All figures are model calculations under the assumptions stated above; no instrument, product or strategy is recommended, and no return is promised. For decisions about your own money, consult an adviser licensed for your situation.