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Simple Interest Loan Calculator

Most auto loans and many personal loans use simple interest — interest accrues daily on the current balance. This calculator computes the scheduled payment, total cost, and how extra payments reduce interest and shorten the term.

Principal

Annual rate

Term (months)

Extra monthly payment

Scheduled monthly payment

$516

Scheduled total paid

$24,790

Scheduled interest

$6,290

Months to payoff (with extras)

3 yr 6 mo

Actual interest (with extras)

$2,915

Interest saved by extras

$3,375

How the math works

Simple-interest loans charge interest on the current balance at each payment date. Paying early reduces the balance, which reduces the next month's interest. Unlike amortized loans, extra principal directly accelerates payoff without restructuring the schedule.

Most auto loans, some personal loans, and some business loans use this structure. Read the note — it may say "simple interest" explicitly. Make the distinction: simple-interest with monthly compounding (common) is different from pure simple-interest amortization.

Editorial noteMaintained by EveryCalc - Reviewed June 2026

EveryCalc calculators are designed for fast, practical estimates with transparent inputs and no required account. We use plain formulas, visible assumptions, and related tools so visitors can check the result from more than one angle.

Results are informational only. For financial, tax, legal, medical, construction, or other high-impact decisions, verify the output against primary sources or a qualified professional.

Learn more about our review process on the EveryCalc methodology page.

How this calculator works

What this page estimates

This Simple Interest Loan Calculator is built to give a quick, browser-based estimate for simple interest loan. Most auto loans and many personal loans use simple interest — interest accrues daily on the current balance. This calculator computes the scheduled payment, total cost, and how extra payments reduce interest and shorten the term. The inputs stay on the page during normal use, and the result should be treated as an estimate for planning, comparison, or education rather than professional advice.

Calculation approach

The calculator applies the standard relationship implied by the inputs, then formats the answer so it can be checked and reused. For finance tools, the most important step is using consistent units, rates, time periods, and assumptions before comparing the result with another calculator or outside quote.

Example workflow

For example, start with a realistic value you already know, change one input at a time, and watch how the answer moves. That makes it easier to tell whether the result is being driven by the main amount, the rate, the time period, or a unit conversion.

Practical checks

Use current, real-world numbers when the result affects money, health, tax, or legal decisions.
Run a low, base, and high case when the inputs are estimates.
Check the related calculators below when the next decision depends on a different assumption.

How to interpret the simple interest loan result

Best use

Use the result as a planning number for comparing payments, rates, returns, tax reserves, or cash-flow choices before you request a quote or make a commitment.

Cross-check

Compare the answer with the contract, lender estimate, tax form, brokerage statement, payroll record, or invoice that will control the real-world outcome.

Watch for

Do not rely on a single optimistic rate, return, or fee assumption. Money pages work best when you run low, base, and high cases and keep professional advice separate from the estimate.

This page belongs to the Finance calculator library, so the answer should be read in the context of the decision you are modeling rather than as a universal rule.

Before relying on this simple interest loan estimate

Most calculator mistakes come from the inputs, not the arithmetic. Use this short audit before you reuse the answer in a spreadsheet, quote, application, or important conversation.

Confirm source numbers

Match balances, rates, fees, taxes, income, and payment dates against the lender quote, payroll record, tax form, statement, invoice, or contract.

Separate cash flow from total cost

A lower monthly payment can still cost more over time if fees, interest, taxes, or a longer term are hidden in the structure.

Run conservative cases

Test at least one higher-cost or lower-return case before using the output for a purchase, refinance, investment, loan, or tax decision.

Rerun this page when the rate, price, term, fee, tax rule, income, expense, or expected holding period changes.

How to Use

Enter principal, rate, and term in months.
Enter extra monthly payment if applicable.
Read scheduled monthly, total interest, and savings from extras.

Frequently Asked Questions

What's the formula?

Simple interest = Principal × Rate × Time. A $20k loan at 8% for 3 years: 20,000 × 0.08 × 3 = $4,800 total interest. Monthly payment = (20,000 + 4,800) ÷ 36 = $688.89.

How do extras save interest?

Extra payments reduce the balance earlier, which reduces every future month's interest accrual. $50 extra per month on a typical 5-year auto loan saves several hundred dollars and shortens term 4-6 months.

Are there prepayment penalties?

Some simple-interest loans carry prepayment penalties (especially subprime). Most mainstream auto loans don't. Always check the note before making large lump-sum prepayments.