Compound Interest Calculator

Simple interest is calculated only on the original principal, every single period. If you have ₹100,000 at 8% simple interest, you earn ₹8,000 every year — no more, no less, regardless of how much time passes. Compound interest calculates interest on the principal plus all the interest already accumulated. In year one you earn ₹8,000. In year two you earn 8% of ₹108,000, which is ₹8,640. The difference seems small at first but compounds (literally) over time — after 20 years the compound interest scenario produces roughly 80% more total growth than simple interest at the same rate.

At shorter time horizons and moderate rates, the practical difference between monthly and daily compounding is small — often a fraction of a percent of the total. But the gap widens with larger principals, higher rates, and longer time periods. More importantly, the principle matters for understanding what you're being offered when comparing financial products. A savings account advertising 7% compounded daily delivers a slightly different actual return than one offering 7% compounded monthly, even though both quote "7%." The metric to compare is APY (Annual Percentage Yield), which normalizes for compounding frequency.

It's a quick mental math trick for estimating how long it takes money to double at a given compound interest rate: divide 72 by the annual rate. At 6%, money doubles in 72 ÷ 6 = 12 years. At 9%, it doubles in 8 years. At 12%, it doubles in 6 years. The rule is an approximation — it's most accurate for rates between 6 and 10% — but it's remarkably close to the precise calculation and useful for quick comparisons. You can also run it in reverse: if you want money to double in 8 years, you need an interest rate of about 72 ÷ 8 = 9%.

The same mechanism that grows your investments works against you when you carry a balance on high-interest debt. A credit card at 36% annual interest, compounded daily, is extraordinarily destructive if you're only making minimum payments. The interest accrues on your full balance each day, and if your minimum payment doesn't cover the month's interest, the balance actually grows. This is how people end up trapped in debt spirals — they're not spending more, but the compounding interest keeps adding to what they owe faster than their payments reduce it. High-interest debt is mathematically the investment with the best guaranteed return: paying off a 24% credit card is like earning 24% risk-free.

Because the growth is exponential, not linear, the years at the beginning of the compounding period are the most leveraged. An investor who puts in ₹100,000 at age 25 and earns 10% annually will have roughly ₹1,744,940 by age 65 — forty years of compounding. An investor who waits until 35 to put in the same ₹100,000 will have about ₹672,750 — the ten-year head start is worth more than a million rupees of final wealth from a single identical investment. This math is why the most universally agreed-upon piece of investment advice is simply: start as early as you can.