Published on August 08, 2026 • Last updated August 08, 2026
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Compound interest is interest calculated on both the original amount invested or borrowed and on the interest that has already accumulated, causing a balance to grow faster over time than it would with simple interest.
When you deposit money in a savings account or take out a loan, interest is added at regular intervals — say, every month or quarter. With compound interest, each time that interest is added, it becomes part of the balance that future interest is calculated on — you start earning "interest on interest," not just interest on your original amount. This compounding effect is what makes long-term investing so powerful: in the early years the difference between compound and simple interest is small, but over many years the gap widens dramatically, because every bit of interest earned starts generating its own interest — often summarized as the "snowball effect" of compounding.
Two factors have an outsized effect on growth: compounding frequency (how often interest is added — annually, quarterly, monthly, or daily) and time (how long the money stays invested). More frequent compounding and longer horizons both lead to noticeably higher returns at the same rate. Compound interest isn't limited to investments — it works the same way on debt, which is why unpaid credit card balances can grow faster than expected if left unpaid.
It's the mathematical backbone behind many common financial products, including Fixed Deposits, Recurring Deposits, and retirement growth projections — understanding it explains both why starting to invest early matters so much, and why paying off high-interest debt quickly is so important.
Learn how Compound Interest is calculated
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