Compound Interest Calculator ☆ Save
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Time does more work than the rate
Compounding means your returns start earning returns. Over a few years it is unremarkable; over decades it does something that feels disproportionate — and the dominant variable is time, not the return you assume.
Change only the years in the calculator above and watch the outcome move. A decade you did not use costs more than any fee or rate difference you will ever negotiate, which is why starting small now genuinely beats starting properly later.
Use it to disprove a scam in thirty seconds
This calculator has a second use that is arguably more valuable than the first. Take any promised return and compound it.
A scheme offering "20% a month" turns SDG 10,000 into roughly SDG 89,000 in a year — and about SDG 790,000 in two.
Then ask the obvious question: if anyone could reliably do that, why are they recruiting strangers with a small minimum investment? Returns that would make someone extraordinarily wealthy within a few years are not being shared with people they have never met.
Run the promise through the calculator and believe the arithmetic rather than the person. Watching a pitch become absurd on screen is more persuasive than any warning — and the structural warning signs are consistent: guaranteed returns, urgency, rewards for recruiting others, vague explanations of how the money is made, and withdrawals that suddenly become difficult.
Before committing money to any scheme, check the provider against your market's financial regulator — on a register you found yourself, not through a link they sent you.
Three things that quietly reduce the real result
- Inflation. The calculator projects nominal amounts. What matters is what the sum will buy — so either use a conservative return that approximates a real one, or read the result as "units of currency", not "buying power";
- Tax and fees. Investment returns are usually taxed and always cost something to access. Check what applies locally, and run the projection at two fee levels to see the difference on your numbers rather than trusting a slogan;
- Interruptions. The projection assumes you never stop. In practice people stop when an emergency arrives — which is why an emergency fund protects a long-term plan more effectively than a higher rate does.
What return is realistic?
- Cash and deposits — modest, and often below inflation. See the savings calculator;
- Diversified investments — historically more over long periods, with real volatility and no guarantee;
- Anything guaranteeing far more, with no risk — is not an investment.
Be deliberately conservative. A projection built on an optimistic rate is a wish with a chart, and the decisions you make on the back of it are real.
The highest-return move most households can make
Worth stating plainly because it outranks anything this calculator will show: clearing expensive debt is a guaranteed, risk-free return. Consumer credit typically costs far more than any investment reliably earns. If you carry it, the debt payoff planner is the tool to use before this one.
Frequently asked questions
What rate should I enter?
Something you can defend, after fees. Run a second, lower scenario too — if the plan only works at the optimistic rate, it is not a plan.
Does this account for inflation?
No — it projects nominal amounts. Reduce your assumed return to approximate a real return if you want purchasing power.
Monthly contributions or a lump sum?
Both work. Regular contributions suit how income actually arrives and remove the pressure of timing.
Someone promised me a fixed monthly return.
Put it in the calculator and look at the two-year figure, then check the provider against your regulator's register. Guaranteed high returns do not exist.
Where should the money actually go?
Emergency fund first, then expensive debt, then long-term investing — using any tax-sheltered account your market offers.
Projections assume constant returns and uninterrupted contributions; real returns vary and are not guaranteed. Tax treatment varies by market. General information, not investment advice.