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The detailed guide below is currently available in English.
Simple vs. compound interest
Simple interest pays only on the original principal: $1,000 at 10% earns $100 every year, no matter how long you wait. The formula is I = P × r × t.
Compound interest pays on the principal and on interest already credited, so growth accelerates over time. The balance after t years with n compounding periods per year is P × (1 + r/n)nt. The difference between the two approaches can be dramatic over long periods.
Why compounding frequency matters
A nominal rate of 10% is not always what it seems. Compounded annually it yields exactly 10%; compounded monthly it yields about 10.47%; compounded continuously it yields about 10.52%. That effective figure is the annual percentage yield (APY), and it is the number you should use when comparing accounts.
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When is simple interest used in real life?
Some short-term loans, certain bonds, and car-title or payday-style lending use simple interest. Most savings accounts and investments, by contrast, compound.
What does "continuous compounding" mean?
It is the mathematical limit of compounding every instant, giving a balance of P·e^(rt). Real banks do not compound continuously, but the figure is useful as an upper bound.
How do taxes and inflation change the result?
Taxes are subtracted from interest as it is earned, which slightly slows compounding. The buying-power row then shows what the ending balance spends like in today’s dollars after your inflation rate.