Interest Calculator
Compare simple versus compound interest accrual over variable deposit and lending horizons.
Parameters & Inputs
Summary & Breakdown
Balance Trajectory Over Time
About the Interest Calculator
Interest is the cost of borrowing capital or the reward earned for depositing it. Understanding how interest compounds over time separates successful investors from borrowers paying unnecessary financing fees.
While simple interest calculates yield solely on the original baseline deposit, compound interest reinvests previous earnings into the capital base. As time passes, the growth curve turns exponential.
This calculator contrasts simple interest with compound interest across multiple compounding periods (daily, monthly, quarterly, annually) to illustrate the time value of money.
How the Calculations Work
Compound interest calculates final value using the exponential yield formula, while simple interest follows a linear formula.
Compound: A = P(1 + r/n)^(nt) | Simple: A = P(1 + rt)
Variables & Definitions
- P: Starting principal deposit balance
- r: Annual interest rate expressed as a decimal
- n: Number of times interest is compounded per year
- t: Time elapsed in years
Depositing $10,000 at 7% annual interest for 10 years compounded monthly (n=12): Compound ending balance is $20,096.61 (yielding $10,096.61 in interest). Simple interest on the same deposit earns only $7,000.00, demonstrating a $3,096.61 compounding bonus.
Key Terms Explained
Compounding
The process where an asset€™s earnings, from either capital gains or interest, are reinvested to generate additional earnings.
Annual Percentage Yield (APY)
The real rate of return taking compounding frequency into account, higher than nominal APR.
Rule of 72
A mental rule of thumb stating that 72 divided by the annual interest rate estimates how many years it takes for an investment to double.
Nominal Rate
The advertised interest rate before adjusting for compounding frequency or inflation.
Practical Tips & Pitfalls to Avoid
Start investing early
Compounding exhibits its greatest acceleration in the final years of long horizons. Time in the market matters more than timing.
Check compounding frequency
Daily compounding generates higher returns than quarterly compounding for identical stated interest rates.
Watch the expense ratio
Management fees act like reverse compounding, steadily eroding lifetime portfolio returns.
Reinvest dividends immediately
Always configure dividend reinvestment programs (DRIP) to maximize compounding velocity.
Frequently Asked Questions
A = P(1 + r/n)^(nt), where P is principal, r is the annual rate, n is compounding cycles per year, and t is the time in years.
Compounded monthly, $10,000 grows to $20,096.61, more than doubling your initial investment.
APR reflects the nominal interest rate without compounding. APY reflects the effective annual yield including compounding effects.
Daily compounding produces slightly higher returns because accrued interest begins earning interest after 24 hours rather than 30 days.
Yes. Continuous compounding uses the formula A = P * e^(rt), representing the mathematical limit of infinite compounding.