What is Interest Calculator?
An interest calculator determines the total dollar return or financing expense accrued on a principal balance based on rate, time, and compounding cycles.
How to Use This Calculator
- Enter the starting principal balance.
- Specify the annual interest rate.
- Select duration in years.
- Choose compounding frequency to see exact compound earnings vs simple interest.
The Mathematical Formula & Variables
A = P * (1 + r/n)^(n*t)
Variables Definition
| Symbol / Variable | Name | Description |
|---|---|---|
A |
Final Balance | Principal plus all accumulated interest. |
P |
Principal | Initial deposit. |
r |
Annual Rate | Nominal interest rate as a decimal. |
n |
Compound Cycles | Times compounded per year. |
t |
Time | Investment length in years. |
Step-by-Step Worked Example
Scenario: $10,000 deposited for 5 years at 6% interest compounded monthly.
- r = 0.06, n = 12, t = 5.
- Base = 1 + (0.06 / 12) = 1.005.
- Exponent = n * t = 12 * 5 = 60 periods.
- Growth = (1.005)^60 = 1.34885.
- Final balance A = $10,000 * 1.34885 = $13,488.50.
- Total Interest = $13,488.50 - $10,000 = $3,488.50.
Result: Ending balance is $13,488.50 with $3,488.50 earned interest.
Frequently Asked Questions
How does compound interest differ from simple interest?
Simple interest is earned solely on the original principal. Compound interest earns interest on prior interest, growing exponentially faster over time.
What is the Rule of 72?
The Rule of 72 estimates how many years it takes to double your money: divide 72 by your annual interest rate (e.g., at 6%, your money doubles in ~12 years).