What is the Compound Interest Calculator?
The Compound Interest Calculator shows how your money grows when interest is earned on both the initial principal and the accumulated interest from previous periods. Albert Einstein reportedly called compound interest the eighth wonder of the world. This calculator helps you understand the exponential growth potential of your investments.
How does it work?
Enter your initial principal, annual interest rate, time period, and how often interest compounds per year. The calculator applies the compound interest formula A = P(1 + r/n)^(nt), where P is principal, r is the annual rate, n is compounds per year, and t is time. The result shows both the future value and the total interest earned.
Formula
A = P x (1 + r/n)^(n x t)
How the calculation works
How the calculation works
- 1Divide the annual rate by the compounding frequency to get the per-period rate: r / n
- 2Multiply the frequency by the time in years to get the total periods: n x t
- 3Raise (1 + r / n) to the power of n x t
- 4Multiply the result by the principal: A = P x (1 + r/n)^(n x t)
- 5Interest earned = A - P
Worked example
Worked Example
Sara deposits Rs 10,000 in a bank fixed deposit at 8% per annum, compounded monthly, for 5 years.
- 1Step 1: Per-period rate = 0.08 / 12 = 0.006667
- 2Step 2: Total periods = 12 x 5 = 60
- 3Step 3: Growth factor = (1.006667)^60 = 1.48985
- 4Step 4: Future value = 10,000 x 1.48985 = Rs 14,898.46
- 5Step 5: Interest earned = 14,898.46 - 10,000 = Rs 4,898.46
Result
Sara's deposit matures at Rs 14,898.46, earning Rs 4,898.46 in interest - Rs 898.46 more than the Rs 4,000 she would have earned with simple interest at the same rate.
Interpretation guide
How to read your result
Compounding adds only modestly over simple interest in this window
Short-term money belongs in low-risk deposits; do not chase high rates for short goals
The compounding gap becomes visible, especially with monthly compounding
Use 80C-eligible instruments or diversified funds depending on your goal and risk appetite
The exponential effect dominates - most of the final value comes from interest, not principal
Maximize time in the market; even small monthly additions compound into large sums
Common mistakes
- - Assuming compound interest grows linearly when it actually grows exponentially
- - Ignoring the effect of taxes on interest earned
- - Choosing annual compounding when more frequent compounding yields higher returns
Practical tips
Practical tips
Prefer monthly or daily compounding over annual compounding when comparing deposits; the same rate compounds to a visibly larger sum
Use the Rule of 72 to sanity-check: divide 72 by the rate to estimate doubling time, so 8% doubles money in about 9 years
Remember that FD interest above Rs 40,000 a year (Rs 50,000 for senior citizens) attracts TDS before it reaches your account
Consider tax-saver FDs with 5-year locks under Section 80C if you need deductions more than liquidity
Reinvest interest instead of withdrawing it, otherwise you lose the compounding effect entirely
Compare the effective annual yield rather than the headline rate when choosing between banks and NBFCs
When should you use it?
- - Comparing savings accounts and fixed deposits with different compounding frequencies
- - Projecting long-term investment growth for retirement planning
- - Understanding the impact of compound frequency on total returns
- - Teaching the power of compounding to students or new investors
Benefits
- - Visually demonstrates exponential growth versus linear growth
- - Helps compare different compounding frequencies side by side
- - Motivates early investing by showing the time value of money
Step-by-step example
Start with your initial investment amount. Determine the annual interest rate your investment or savings account offers. Choose how frequently interest compounds daily, monthly, quarterly, or annually. Enter the number of years you plan to invest. The calculator shows your final balance and how much of it came from interest.
Real-world example
Investing Rs 10,000 at 8% annual interest compounded monthly for 5 years grows to Rs 14,898. The total interest earned is Rs 4,898. With simple interest at the same rate, you would earn only Rs 4,000, so compounding gives you Rs 898 extra.