Simple Interest Calculator
Compute straight-line simple interest yields.
Total Interest Earned
$1,500.00
Popular Interest Calculations
How to Use
Enter the principal amount
Input the original loan amount or investment capital before any interest is added.
Enter the annual interest rate
Input the yearly rate as a percentage (e.g., 6 for 6% per annum).
Set the time period
Enter duration in years. For months, divide by 12 (e.g., 18 months = 1.5 years).
Review total interest and final amount
The calculator shows interest earned/owed and principal plus interest combined.
Simple Interest Formula
Simple interest is calculated by multiplying the principal amount by the interest rate and the time period. Unlike compound interest, you do not earn interest on your interest.
Frequently Asked Questions
What are common examples of simple interest?
Personal loans, auto loans, and short-term corporate loans often use simple interest. It is also used by certain fixed-income bonds to calculate coupon payments.
Real-World Examples & Use Cases
Personal Loans & Installment Lending
Many personal loans and consumer installment loans use simple interest, where charges accrue only on the remaining outstanding principal balance. As borrowers make monthly payments, the principal decreases, and so does the daily interest charge. This differs from compound interest loans where unpaid interest may capitalize. Understanding simple interest helps borrowers calculate total repayment cost and benefit from making extra principal payments that immediately reduce future interest charges.
Treasury Bills & Short-Term Investments
Government treasury bills, fixed deposits with short durations, and certificates of deposit often pay simple interest for given terms. Investors comparing a 6-month T-bill yielding 5% simple against a savings account with daily compounding need to calculate equivalent returns for fair comparison. Simple interest calculations are the starting point for evaluating these instruments before deciding whether to lock funds in for 30, 90, or 180 days.
Auto Loans
Most auto loans in the United States calculate interest using a daily simple interest method, where interest accrues daily on the outstanding principal balance. Paying your car loan early or making an extra payment immediately reduces the principal, decreasing the next month's interest charge. A car loan calculator using simple interest shows exactly how much total interest you pay over the loan term and the direct financial benefit of making biweekly instead of monthly payments.
Student Loans During Grace Periods
Unsubsidized federal student loans accrue simple interest from the date of disbursement, even during in-school and grace periods. If you do not pay interest while in school, the accumulated simple interest capitalizes (adds to principal) when repayment begins. Understanding how much simple interest accrues during a 4-year degree on $30,000 of unsubsidized loans at 7% helps students decide whether to make small interest-only payments during school to prevent future balance inflation.
How It Works
Simple interest uses a direct proportional formula: SI = P × R × T Where: - SI = Simple Interest earned or charged - P = Principal (original amount) - R = Annual interest rate (as a decimal; divide percentage by 100) - T = Time in years Final Amount (A) = P + SI = P(1 + RT) Examples: - $10,000 at 5% for 3 years: SI = 10,000 × 0.05 × 3 = $1,500 - Total: $11,500 - $5,000 at 8% for 6 months (0.5 years): SI = 5,000 × 0.08 × 0.5 = $200 - Total: $5,200 Key property: Interest is always calculated on the ORIGINAL principal, not on accumulated balances. This means simple interest grows linearly, not exponentially.
Frequently Asked Questions
What is the formula for simple interest?▼
How does simple interest differ from compound interest?▼
Is simple or compound interest better for borrowers?▼
How do you convert monthly interest rate to annual for simple interest?▼
What is the difference between simple interest and flat rate interest?▼
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