Simple Interest Calculator
Calculate simple interest, total repayment, and loan cost in seconds — built for personal loans, student loans, auto loans, and short-term borrowing in the U.S. and worldwide.
Loan / Investment Details
= $50,000 × 8% × 3 ÷ 100
Try $50,000 at 8% for 3 years to instantly see your interest breakdown.
What is Simple Interest?
Simple interest is calculated only on the original principal amount — not on previously earned interest. The interest amount stays flat every period because the base never changes. That makes it predictable, transparent, and easy to plan for, which is why it shows up in personal loans, student loans, auto loans, and most short-term borrowing in the United States and elsewhere.
Unlike compound interest — which earns on a growing balance — simple interest always refers back to the original principal. For borrowers, this means lower total repayment over short durations compared with compounding products. If you want to compare a full amortized payment to flat interest, see our loan calculator.
Simple Interest Formula
SI
Simple Interest
P
Principal
R
Annual Rate (%)
T
Time in Years
Example: $50,000 at 8% per year for 3 years → SI = 50,000 × 8 × 3 ÷ 100 = $12,000. Total repayment = $62,000.
Where Simple Interest Is Used
Personal Loans
Most U.S. banks, credit unions, and online personal lenders calculate interest as a flat or reducing-balance figure on the outstanding principal — a direct application of the simple interest model.
Student Loans
Federal student loans (Direct Subsidized / Unsubsidized) and most private student loan providers accrue interest on the original disbursed amount using a daily simple-interest method.
Auto Loans
Auto lenders typically quote APR but apply daily simple interest on the outstanding balance, which is why making payments earlier in the month can reduce total interest.
Small Business Financing
SBA microloans, working-capital lines from community banks, and merchant-cash short-term advances frequently use simple interest for predictable repayment plans.
Short-Term Lending
Bridge loans, family / friends notes, payday alternatives, and short consumer installment loans use flat simple interest because the durations are too short for meaningful compounding.
Simple vs Compound Interest
Simple interest stays flat — the same amount every period. Compound interest grows every period because interest is added to the principal. The gap between the two widens with time.
| Year | Simple Interest (Total) | Compound Interest (Total) |
|---|---|---|
| Year 1 | $110,000 | $110,471 |
| Year 2 | $120,000 | $122,039 |
| Year 3 | $130,000 | $134,818 |
| Year 5 | $150,000 | $164,531 |
| Year 10 | $200,000 | $270,704 |
$100,000 at 10% per year — simple interest vs monthly-compounding interest.
Loan Examples
Loan Type
Personal Loan
Principal
$10,000
Rate
8%
Interest
$2,400
Total Repayment
$12,400
Loan Type
Student Loan
Principal
$25,000
Rate
6%
Interest
$6,000
Total Repayment
$31,000
Loan Type
Auto Loan
Principal
$30,000
Rate
7%
Interest
$10,500
Total Repayment
$40,500
These are flat simple-interest estimates. Real auto and student loans typically amortize, so monthly payments include both principal and interest — use our loan calculator or mortgage calculator for those.
How U.S. Lenders & Banks Use Simple Interest
Banks and lenders apply simple interest where flat, predictable cost matters most — usually on the borrowing side. On the savings side, they prefer compound interest to attract deposits.
Borrower side (simple interest common)
- •Personal loans from banks, credit unions, and online lenders
- •Federal and private student loans (daily simple interest)
- •Auto loans from banks, credit unions, and captive finance arms
- •SBA microloans and short-term small-business financing
- •Bridge loans, family loans, and payday alternatives
Depositor side (compound interest typical)
- •High-yield savings accounts (compound daily, paid monthly)
- •Certificates of deposit / CDs (compound monthly or annually)
- •Money market accounts (compound monthly)
- •U.S. Treasury I-Bonds (compound semi-annually)
Trusted by students, borrowers, and financial planners worldwide.
Methodology reviewed by an Accredited Financial Counselor (AFC®). See our methodology and editorial policy. Want to convert a simple-interest rate into an effective annual yield? Try our percentage calculator.
Frequently Asked Questions
Want long-term investment projections? Try our Compound Interest Calculator →
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