Interest basics
Simple vs compound interest: compare growth with an example
See why reinvesting interest changes the final amount and how compounding frequency affects a long-term estimate.
Updated August 5, 2026 · 5 min read
Simple interest uses the original principal
Simple interest is principal multiplied by the annual rate and time. At ₹1,00,000, 8% per year, and 10 years, the simple interest is ₹80,000 and the final amount is ₹1,80,000.
The calculation adds the same ₹8,000 for each full year because later interest is not calculated on earlier interest.
Compound interest grows the balance used next time
With compounding, each credited interest amount becomes part of the balance for later periods. At the same principal, nominal rate, and 10-year period, monthly compounding produces a higher estimate than simple interest.
The gap grows because interest begins earning interest. More time and a higher positive rate generally make this difference more visible.
Compounding frequency matters
Annual compounding credits interest once per year, while monthly compounding divides the nominal rate across 12 periods. At the same positive nominal rate, more frequent compounding produces a slightly higher final amount.
Use the frequency stated in the product terms. Do not substitute monthly compounding merely because contributions or repayments happen monthly.
Keep product charges and cash flows separate
The comparison assumes one principal, a constant rate, and no tax, fees, withdrawals, or additional deposits. Investments and loans may use different day-count methods and crediting rules.
Use the result to understand the calculation, then compare the actual disclosed maturity or repayment amount when choosing a financial product.
Put this guide into practice
Use the related calculators
Put the steps in this guide into practice with a focused calculator, then return here to check an assumption or compare another scenario.