Simple Interest Calculator
Simple interest calculator: interest on a principal amount at a fixed annual rate, with no compounding.
Editorial review: Farrow (pseudonym; identity and professional credentials are not disclosed). This page is for educational purposes, not professional advice.
Your inputs
Results update as you type. Nothing you enter leaves your device.
Results
- Total amount
- $11,500.00
Example with the starting values
These results use the calculator's initial inputs. Change the values above to calculate your own estimate.
Inputs
- Principal
- 10000 $
- Annual rate
- 5 %
- Years
- 3
Results
- Interest
- $1,500.00
- Total amount
- $11,500.00
How does the Simple Interest Calculator work?
Simple interest is interest charged or earned only on the original principal, never on past interest. The formula is I = P × r × t: principal times annual rate (as a decimal) times years.
The total amount is A = P + I = P(1 + r·t). For example, $10,000 at 5% for 3 years earns $10,000 × 0.05 × 3 = $1,500, for a total of $11,500.
Frequently asked questions
How do I calculate simple interest?
Multiply the principal by the annual rate and the number of years. For $5,000 at 4% for 2 years, I = 5,000 × 0.04 × 2 = $400.
What is the difference between simple and compound interest?
Simple interest is paid only on the principal, while compound interest is also paid on earned interest. $1,000 at 5% for 10 years earns $500 simple but about $629 compounded yearly.
How do I calculate simple interest for months or days?
Convert the time to years first: 6 months is 0.5 and 90 days is 90 / 365. $2,000 at 6% for 6 months earns 2,000 × 0.06 × 0.5 = $60.
Where is simple interest used in the US?
Many auto loans, some personal loans, and US Treasury bills and notes use simple interest calculations.