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Compound Interest

Calculate compound interest growth

By UtilityKit Team · Reviewed for accuracy by UtilityKit Editors · Updated May 2026

About Compound Interest

Compound interest is the mechanism by which earned interest itself begins to generate further interest over time, producing exponential rather than linear growth. This calculator applies the standard formula A = P(1 + r/n)^(nt) — where P is principal, r is annual rate, n is compounding frequency, and t is time in years — to project how a lump sum or ongoing deposit programme grows across any time horizon. You can choose compounding frequencies of daily, monthly, quarterly, semi-annual, or annual to match real-world savings accounts, fixed deposits, or bond products. An optional recurring contribution field lets you model systematic investment plans (SIPs), recurring deposits, or 401(k)-style monthly contributions on top of the initial principal.

Why use Compound Interest

Accurate Compounding Frequencies

Choose daily, monthly, quarterly, semi-annual, or annual compounding to match exactly how your bank or fund calculates returns. Different frequencies produce meaningfully different final balances over long horizons.

Recurring Contribution Support

Add a monthly SIP or recurring deposit amount to the lump sum. The tool handles both the compound growth on principal and the rolling additions, which together represent most real-world savings scenarios.

Year-by-year Growth Table

An expandable breakdown shows the cumulative balance, interest earned that year, and total contributions at every annual checkpoint. This makes the exponential curve tangible rather than just a final number.

Standard Formula Transparency

The calculator uses A = P(1 + r/n)^(nt), the same formula banks and financial textbooks use. Seeing the formula alongside the result builds confidence in the output and makes it easy to verify.

Inflation Adjustment Toggle

Enter an expected annual inflation rate to convert the nominal projected balance into a real purchasing-power equivalent. This is essential for any projection longer than five to ten years.

Complete Privacy

Salary, investment, and savings figures are sensitive. All computation happens in your browser with no server calls, no cookies, and no data storage of any kind.

How to use Compound Interest

  1. Enter your starting principal — the lump sum you are investing or depositing today
  2. Enter the annual interest rate as a percentage, for example 7 for 7% per year
  3. Select the compounding frequency: daily, monthly, quarterly, semi-annual, or annual
  4. Set the time horizon in years — how long the money stays invested or deposited
  5. Optionally enter a recurring monthly contribution to model SIP or 401(k)-style deposits
  6. Review the final balance, total interest earned, and the year-by-year amortisation table

When to use Compound Interest

  • When planning how much a current savings account or fixed deposit balance will grow to by retirement age
  • When comparing two investment products with different quoted interest rates and different compounding frequencies
  • When calculating how a monthly SIP or recurring deposit programme will grow over a five-, ten-, or twenty-year horizon
  • When a student wants to understand the compound interest concept for an exam problem or finance assignment
  • When evaluating whether to invest a lump sum now versus spreading it across monthly deposits over time
  • When projecting college savings or a child's education fund to estimate whether current contributions are on track

Examples

Lump-sum savings, 10 years

Input: Principal: $10,000, Rate: 7% annual, Compounding: yearly, Years: 10

Output: Final: $19,672 — Interest earned: $9,672

Monthly compounding, long term

Input: Principal: ₹500,000, Rate: 8%, Compounding: monthly, Years: 15

Output: Final: ₹1,654,929 — Interest: ₹1,154,929

With monthly SIP contribution

Input: Principal: $5,000, Rate: 6%, Years: 20, Monthly add: $200

Output: Final: $107,389 — Contributions: $53,000, Interest: $54,389

Tips

  • Time in the market matters more than rate — starting five years earlier often beats earning an extra percentage point of return
  • Use the Rule of 72 to sanity-check results: divide 72 by the rate to estimate years to double your money
  • Toggle the inflation adjustment for any projection beyond ten years — nominal numbers can be misleadingly large
  • For SIPs and mutual fund projections, set compounding to monthly, which matches how most fund NAVs are calculated
  • Subtract your marginal tax rate from the headline interest rate when comparing taxable and tax-exempt products

Frequently Asked Questions

What is the compound interest formula?▾
The standard formula is A = P(1 + r/n)^(nt), where A is the final amount, P is principal, r is the annual interest rate as a decimal, n is the number of compounding periods per year, and t is the number of years. The result A includes both the original principal and all accumulated interest.
How does compounding frequency affect returns?▾
More frequent compounding means interest is calculated and added to the balance more often, so it starts earning its own interest sooner. The difference between annual and daily compounding is small for short periods but becomes significant over decades. Moving from annual to monthly compounding on a 7% rate adds roughly 0.23 percentage points to the effective annual yield.
What is the difference between simple and compound interest?▾
Simple interest is calculated only on the original principal throughout the entire term: Interest = P × r × t. Compound interest is calculated on the growing balance, so each period's interest is added to the principal before the next period's calculation. Over time, compound interest generates dramatically more growth than simple interest at the same rate.
What is the Rule of 72?▾
The Rule of 72 is a quick mental shortcut: divide 72 by the annual interest rate to estimate how many years it takes to double your money. For example, at 8% per year, money doubles in approximately 9 years (72 ÷ 8). The rule is most accurate for rates between 6% and 10%.
Should I use nominal or real inflation-adjusted returns?▾
Nominal returns show how much your money grows in absolute number terms. Real returns subtract inflation to show how much purchasing power you actually gain. For long-term planning — retirement, education funds — real returns are more meaningful because they reveal whether you are actually getting richer or just keeping pace with rising prices.
How are SIP or recurring contributions handled?▾
Each monthly contribution is treated as a new sub-principal that starts compounding from the month it is added. The total future value of a series of equal monthly contributions is the sum of each contribution's individual compound growth, which follows an annuity formula layered on top of the lump-sum calculation.
Why is daily compounding only marginally better than monthly?▾
The incremental benefit of more-frequent compounding diminishes rapidly as frequency increases. Going from annual to monthly compounding provides a meaningful boost, but moving from monthly to daily adds only fractions of a percent annually. At a 7% annual rate, the difference between daily and monthly compounding over 30 years is well under 0.5%.
Does this account for taxes on interest?▾
The calculator shows gross pre-tax growth. In most jurisdictions, interest, dividends, and capital gains are taxed annually. To get a net-of-tax estimate, subtract your expected tax rate from the interest rate before entering it. For example, at a 20% tax rate on a 7% return, enter 5.6% as the effective rate.

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Glossary

Principal (P)
The original sum of money deposited, invested, or borrowed before any interest is applied. In compound interest calculations, the principal grows each compounding period as interest is added to it.
Annual Rate (r)
The stated yearly interest or return rate expressed as a decimal or percentage. In the compound interest formula, this rate is divided by the compounding frequency n to get the per-period rate.
Compounding Frequency (n)
The number of times per year that interest is calculated and added to the balance. Common values are 1 (annual), 12 (monthly), and 365 (daily). Higher frequency increases the effective annual yield slightly.
Time in Years (t)
The total duration of the investment or deposit in years. Because compound interest grows exponentially, doubling t more than doubles the final balance at any positive rate.
Effective Annual Rate (EAR)
The actual annual return after accounting for intra-year compounding. EAR = (1 + r/n)^n − 1. It is always higher than the nominal annual rate when n is greater than 1, and is the fairest basis for comparing products with different compounding schedules.
Compound Interest Formula A = P(1 + r/n)^(nt)
The standard formula relating final amount A to principal P, annual rate r, compounding frequency n, and time in years t. It is the foundation of savings account, fixed-deposit, and bond growth calculations worldwide.