Calculate how much simple interest you'll earn on your savings or pay on your loan. Use the formula I = P × r × t with step-by-step breakdowns and real-world examples.
I = Interest earned or paid
P = Principal (initial amount)
r = Annual interest rate (in decimal form, e.g., 5% = 0.05)
t = Time period in years
A = Total amount (principal + interest)
P = Principal
r = Annual interest rate (decimal)
t = Time in years
💡 Note: Unlike compound interest, simple interest is calculated only on the principal amount. Interest does not earn interest. Simple interest grows linearly, while compound interest grows exponentially.
Personal loans, auto loans, and payday loans with terms under one year often use simple interest. The shorter the term, the more likely simple interest is applied.
Many CDs pay simple interest at maturity, especially shorter-term CDs (under 1 year). The interest is calculated on the principal and paid out at the end of the term.
Short-term government securities like T-bills (maturity under 1 year) use simple interest. The interest is paid at maturity, calculated on the face value.
Some auto loans use simple interest, where interest accrues daily based on the outstanding principal. Paying early can reduce the total interest paid.
Private loans between individuals and businesses often use simple interest for clarity and ease of calculation, especially for short durations.
Simple Interest: Calculated only on the principal. I = P × r × t. Linearly growing.
Compound Interest: Calculated on the principal AND previously earned interest. A = P(1 + r/n)^(nt). Exponentially growing.
Best for Borrowers: Simple interest is generally cheaper for borrowers because interest doesn't accrue on interest.
Best for Lenders: Compound interest benefits lenders/investors more, as interest generates additional interest over time.
Simple interest is a straightforward method of calculating the interest charge on a loan or the return on an investment. It is called "simple" because it is calculated only on the original principal amount — the initial sum of money borrowed or invested. Unlike compound interest, simple interest does not take into account any interest that accumulates over time.
Simple interest is widely used in financial products where the term is short or where the interest is paid out periodically rather than reinvested. It provides clarity and predictability, making it easy for borrowers and lenders to understand exactly how much interest will be paid or earned.
Determine the initial amount of money — the principal. This is the amount you are borrowing, investing, or depositing. For example, if you deposit $10,000 into a savings account, your principal is $10,000.
Find the annual interest rate expressed as a percentage. Convert it to decimal form by dividing by 100. For example, 5% becomes 0.05. This represents the proportion of the principal that will be paid as interest each year.
Determine how long the money will be invested or borrowed, measured in years. If the time period is in months, divide by 12. If in days, divide by 365 (or 360 for some financial instruments). For example, 6 months = 0.5 years.
Multiply all three values together: I = P × r × t. The result is the total simple interest earned or paid over the entire time period. Add this to the principal to get the total amount: A = P + I.
Problem: You invest $10,000 at 5% simple interest for 3 years.
Interest Earned: $1,500
Total Amount: $10,000 + $1,500 = $11,500
Monthly Interest: $1,500 ÷ 36 = $41.67
Understanding the difference between simple and compound interest is crucial for making informed financial decisions. While simple interest is calculated only on the principal, compound interest is calculated on both the principal and any accumulated interest.
Interest is earned only on the original principal. Growth is linear.
Interest is earned on both the principal and previously accumulated interest. Growth is exponential.
💡 Remember: Unlike compound interest, simple interest is calculated only on the principal. This means your interest does not earn interest — the growth is steady and predictable, but not accelerating.
⚠️ Disclaimer: This calculator is for educational and illustrative purposes only. It does not constitute financial advice. Consult a financial professional before making investment decisions. Actual interest rates, terms, and conditions vary by lender, financial institution, and jurisdiction. Simple interest calculations assume the full principal is held for the entire time period without any additional deposits or withdrawals.