Interest Calculator

Calculate and compare simple vs compound interest for any principal, rate, and time period.

Simple Interest Inputs

1%30%
1 yr30 yrs
Formula: SI = (P × R × T) / 100
SI = (1,00,000 × 8 × 3) / 100 = ₹24,000

Simple Interest Earned

₹24,000

Total Amount

₹1,24,000

Annual Return

8%

Growth

+24% over 3 years

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Interest Calculator Formula & How It Works

Simple: A = P(1 + rt) | Compound: A = P(1 + r/n)^(nt)
  • P = Principal
  • r = Annual interest rate (decimal)
  • t = Time in years
  • n = Compounding frequency (1=annual, 12=monthly, 365=daily)

Interest represents the cost of borrowed money or the reward for saving. Simple interest grows linearly; compound interest grows exponentially because earned interest is reinvested. The more frequently interest compounds, the faster the growth — daily compounding slightly outperforms monthly.

Interest Calculator FAQs

How do I calculate interest on a savings account?

Most savings accounts use compound interest. A = P × (1 + r/n)^(nt). A $10,000 deposit at 4.5% APY compounded monthly for 5 years: A = $10,000 × (1 + 0.045/12)^60 = $12,507.

What is APY vs APR for savings accounts?

APR (Annual Percentage Rate) is the stated interest rate. APY (Annual Percentage Yield) accounts for compounding frequency and represents the actual annual return. APY ≥ APR. Banks advertise APY for savings to show a higher number.

How long does it take money to double?

Use the Rule of 72: Doubling Time ≈ 72 ÷ Annual Rate. At 6%, money doubles in ~12 years. At 10%, in ~7.2 years. This works for compound interest. Simple interest takes exactly 100 ÷ rate years to double.

Related Calculators

Simple Interest Calculator

Calculate simple interest and total amount using the SI = P × R × T formula.

Compound Interest Calculator

Watch your money grow on itself — choose any compounding frequency and see the year-by-year breakdown.

Savings Calculator

Calculate savings growth with regular deposits, or find monthly savings needed to reach your goal.

Future Value Calculator

Calculate the future value of any investment, savings plan, or regular payment series.