Interest Calculator
Comprehensive interest calculator supporting both simple and compound interest calculations with multiple compounding frequencies. Calculate interest earned on savings, loans, or investments with options for annual, semiannual, quarterly, monthly, weekly, or daily compounding. Features detailed results showing interest earned, total amount, and the difference between simple and compound interest. Perfect for comparing investment options, understanding loan costs, or planning savings growth. Includes step-by-step formula explanations and the ability to copy detailed results. All calculations are performed instantly in your browser with complete privacy.
Interest Calculator
Results
Simple Interest
Compound Interest
Compound interest earns $262.82 more than simple interest
Formulas Used:
Simple Interest: I = P × R × T
Compound Interest: A = P(1 + r/n)^(nt)
Where P = Principal, R = Rate, T = Time, n = compounding frequency
What Is an Interest Calculator?
An interest calculator finds the total interest earned or owed on a principal amount based on rate, time, and compounding frequency. It handles both simple interest (I = P×r×t) and compound interest (A = P×(1 + r/n)^(n×t)), letting you compare how different rates, terms, and compounding schedules affect total cost or growth.
Use it to estimate savings account growth, understand how much interest you’ll pay on a loan, or compare the true cost of different financing offers side by side.
How to Use This Interest Calculator
- Enter the principal (starting amount).
- Enter the annual interest rate as a percentage.
- Enter the time period in years.
- Select the compounding frequency (annual, monthly, daily, etc.).
- See total interest and final balance instantly.
Worked Example: $10,000 at 4.5% for 10 Years
| Years | Simple Interest | Compound (Annual) | Compound (Monthly) |
|---|---|---|---|
| 1 | $450 | $450 | $459 |
| 3 | $1,350 | $1,412 | $1,440 |
| 5 | $2,250 | $2,462 | $2,512 |
| 10 | $4,500 | $5,530 | $5,665 |
Over 10 years, monthly compounding adds $135 more than annual compounding on the same $10,000 at 4.5% — and $1,165 more than simple interest. The gap widens at higher rates and longer terms.
Compounding Frequency: How It Affects Your Returns
| Compounding | Times per Year (n) | $10,000 at 5% for 10 yrs |
|---|---|---|
| Annual | 1 | $16,288.95 |
| Quarterly | 4 | $16,436.19 |
| Monthly | 12 | $16,470.09 |
| Daily | 365 | $16,486.65 |
APR vs. APY: What’s the Difference?
APR (Annual Percentage Rate) is the simple annual rate without compounding. APY (Annual Percentage Yield) accounts for compounding and reflects the actual return. APY is always ≥ APR for the same underlying rate.
Formula: APY = (1 + APR/n)^n − 1. At 5% APR compounded monthly: APY = (1 + 0.05/12)^12 − 1 = 5.116%. Savings accounts advertise APY; loans often disclose APR. Always compare the same metric when evaluating financial products.
Tips for Using Interest to Your Advantage
- Start early: At 7% compounded annually, $5,000 grows to $19,671 over 20 years and $38,697 over 30 years. Time is the most powerful variable.
- Compare APY, not APR: High-yield savings accounts advertise APY. Use APY when comparing savings rates.
- For loans, compare total interest cost: A lower rate over a longer term may cost more total interest than a higher rate over a shorter term.
- Extra payments reduce interest dramatically: On a compound-interest loan, paying extra reduces the principal that future interest is calculated on.
Frequently Asked Questions About Interest
How much interest does $10,000 earn in a year at 5%?
Simple: $10,000 × 0.05 = $500. Compounded monthly: $10,000 × ((1 + 0.05/12)^12 − 1) ≈ $511.62.
What is the Rule of 72?
Divide 72 by the annual interest rate to estimate how many years it takes to double your money. At 6%: 72 ÷ 6 = 12 years. At 9%: 72 ÷ 9 = 8 years. It’s a quick mental shortcut for compound growth.
What is the difference between interest rate and APY?
The interest rate (APR) is the nominal annual rate. APY includes the effect of compounding, so it’s slightly higher for the same underlying rate. A 5% APR compounded monthly = 5.116% APY. Always compare APY when evaluating savings accounts.
Related Calculators
- Simple Interest Calculator — I = PRT without compounding
- Loan Calculator — monthly payments and amortization schedule
- Percentage Increase Calculator — percent change and growth rates