Calculator
Compound Interest Calculator
Compound interest is interest earned on both your original money and the interest already added — the engine behind long-term wealth. This calculator shows how a one-time investment grows over time at a chosen rate and compounding frequency, separating your principal from the interest earned. Use it to understand FDs, bonds, or any lump-sum investment, and to see why starting early matters far more than the exact rate you earn.
The lump sum you invest today.
How often interest is added to the balance.
Growth over time
- Principal
- Interest
Assumes a constant rate and no withdrawals or additional deposits. Interest on FDs and most debt instruments is taxable as per your slab; this figure is pre-tax.
What your result means
- Notice how the interest portion grows faster than the principal over time — that acceleration is the whole point of compounding.
- Time matters more than the amount: starting five years earlier usually beats investing a larger sum later.
- A small change in the rate becomes a large change in the maturity over long periods — which is why fees and a percent or two of extra return matter so much.
How to use this calculator
- Enter the lump sum you plan to invest.
- Enter the annual interest rate offered.
- Set the number of years you will stay invested.
- Pick how often interest compounds — quarterly for most Indian FDs.
- Compare the interest earned against the principal to feel the effect of time.
The formula
A = P × (1 + r/k)^(k × t), where A = maturity value, P = principal, r = annual rate (as a decimal), k = compounding periods per year, and t = years. Interest earned = A − P.
Worked example
₹1,00,000 invested at 8% per year, compounded quarterly (k = 4) for 10 years: A = 1,00,000 × (1 + 0.08/4)^(40) ≈ ₹2,20,800. So ₹1,20,800 is interest. The same amount at simple interest would earn only ₹80,000 — the extra ₹40,800 is compounding at work. Over 25 years the gap widens to lakhs.
When to use it
- Estimating the maturity value of a fixed deposit or bond.
- Understanding how compounding frequency changes the final amount.
- Demonstrating to yourself why early investing beats a higher rate started later.
- Comparing a lump-sum investment against the same money left idle.