Revolving vs Installment Loans: How They Work

Revolving loans let you borrow, repay and borrow again up to a credit limit; installment loans provide a set amount that you repay on a schedule. This calculator estimates the monthly payment and total interest for a fixed-rate installment loan from its amount, APR and term, so you can examine one side of the comparison with clear assumptions.

Formula

The calculator uses the standard fixed-payment loan formula. Let P be the principal in dollars, APR the annual percentage rate in percent, r the monthly rate as a decimal, and n the number of monthly payments. It calculates:

• Monthly rate: r = APR / 1200.
• Number of payments: n = years × 12.
• Monthly payment: M = P × r / [1 − (1 + r)⁻ⁿ].
• Total interest: I = rounded monthly payment × n − P.

The payment is displayed to the nearest cent. Total interest uses that rounded payment, so it reflects the calculator’s scheduled-payment arithmetic; a lender’s final payment can differ because of rounding, payment dates or contract terms.

Worked Example

Using the calculator’s default inputs—$20,000 principal, 8% APR and a five-year term:

1. Convert the APR to a monthly decimal rate: 8 / 1200 = 0.0066667.
2. Convert the term to payments: 5 × 12 = 60 months.
3. Substitute into the payment formula: $20,000 × 0.0066667 / [1 − (1.0066667)⁻⁶⁰] = approximately $405.53 per month.
4. Calculate total interest using the rounded payment: $405.53 × 60 − $20,000 = $4,331.80.

The displayed estimate is therefore a $405.53 monthly payment and $4,331.80 in total interest under the stated assumptions.

Assumptions

• The interest rate remains fixed throughout the term.
• Payments are equal monthly payments, made at the end of each monthly period.
• Interest compounds monthly at APR / 12.
• Fees, taxes, insurance, PMI and escrow are not included.

Revolving and Installment Loans Compared

The key difference is how access to borrowed money works. With a revolving account, a lender sets a maximum balance, or credit limit. You can draw funds, repay some or all of the balance, and—if the account remains available—borrow again. A credit card is a familiar example; a line of credit is another. The amount owed and the required payment can change from month to month.

An installment loan generally advances a specified principal amount. You repay it through a sequence of payments over a defined term. Payments commonly include interest and principal, and the outstanding balance declines as principal is paid. Auto, personal and student loans are examples of products that may use installment structures, though terms vary by contract.

• Access: revolving credit can be reused; installment principal is usually received as a lump sum.
• Repayment: revolving payments vary with the balance and account terms; installment payments are often scheduled in advance.
• Balance: revolving balances may rise again after repayment; installment balances normally move toward zero as scheduled payments are made.
• Interest: both can charge interest, but the calculation method, rate structure and fees depend on the agreement.

How the Two Structures Work

Imagine a revolving account with a $5,000 limit. If $1,000 is borrowed and $300 of principal is repaid, the remaining balance is generally $700 before interest and other charges; available credit may increase accordingly. Borrowing again can raise the balance. A credit limit is not a recommendation to borrow the full amount, and account terms determine how much is available.

With a $20,000 installment loan, the borrower receives the principal and follows a repayment schedule. Early payments on an amortizing loan typically devote a larger share to interest because interest is calculated on a higher remaining balance. As the balance falls, the interest portion usually falls too, while the principal portion rises. The schedule and actual allocation depend on the loan’s terms.

Not every loan fits a simple example. Some installment loans have variable rates, irregular payments, balloon payments or fees. Some revolving accounts offer promotional terms or charge different rates for different transaction types. Read the agreement and any payment schedule rather than assuming that labels alone describe every detail.

Costs, Payments and the Calculator’s Limits

For a fixed-rate installment loan with regular payments, this calculator isolates the effect of principal, APR and term. A longer term usually spreads repayment across more months; with the same principal and rate, that generally lowers the scheduled payment but increases the amount of time interest can accrue. The calculator does not model a revolving balance, because that requires additional information such as future purchases, repayments, rate changes and the account’s payment rules.

APR is an annualized rate expressed as a percentage, but the calculator’s formula treats it as a nominal annual rate divided into monthly periods. It assumes no additional charges are financed or paid separately. Ask the lender for the actual APR, payment schedule and any fees or other costs relevant to the specific offer; do not substitute a guessed figure for a disclosed one.

Common errors include entering 8 when the rate is 8% (correct) but treating it as 0.08 in this calculator, entering months in the years field, or comparing payment amounts without considering the different terms and balances. The result is an estimate, not an approval decision or a complete measure of the cost of credit.

Choosing Which Comparison to Make

Rather than comparing labels in isolation, identify the way you expect to use the credit and the figures in each agreement. A revolving facility may suit repeated borrowing and repayment in separate amounts; an installment structure is designed around a specific advance and repayment schedule. Those descriptions do not establish which option is appropriate for a particular person.

• Check whether you need access to funds once or may need to draw repeatedly.
• Compare the amount borrowed, APR, fees, payment rules and repayment timeline on the actual disclosures.
• For revolving credit, consider how new borrowing and changing balances affect the amount owed.
• For installment credit, review whether the payment is fixed, whether the rate can change, and what happens if payments are late or extra payments are made.
• Use consistent assumptions when comparing total costs; a lower monthly payment alone does not mean a lower total repayment.

One misconception is that revolving credit always means a credit card, or that every installment loan has an unchanging payment. These are common examples, not universal definitions. The contract determines the mechanics. Another misconception is that paying down a revolving balance permanently ends the debt; available credit can make it possible to borrow again, so the balance can return.

Frequently Asked Questions

Is a credit card a revolving loan?
It is a common form of revolving credit. You can generally make purchases up to a limit, repay the balance and use available credit again, subject to the account agreement.

Is a personal loan revolving or installment?
A personal loan that provides a fixed amount and a scheduled series of repayments is generally an installment loan. Product terms can vary, so confirm how the specific agreement works.

Which type has a fixed monthly payment?
Installment loans often have a set payment schedule, particularly when the rate is fixed. Revolving payments usually vary with the balance and account terms. Neither pattern is guaranteed by the label alone.

Does revolving credit always cost more?
No universal cost comparison follows from the structure. Rates, fees, balances, payment timing and repayment behavior all matter. Use the actual disclosed terms and a consistent time period to compare costs.

Can an installment loan become revolving?
Not simply because payments are made. An installment loan normally follows its repayment agreement; a separate credit line or a contract change would be needed for access to reusable credit.

This result is an estimate; the lender’s disclosure gives the exact figures.

Related

• Loan Installment Calculator: Estimate Monthly Payments
• Kawasaki Installment Loan Payment Calculator
• Lack of Recent Installment Loan Information?

in p | Loan amount | $ | 20000 | 1 | 100000000
in apr | Interest rate (APR) | % | 8 | 0.01 | 100
in yrs | Loan term | years | 5 | 0.0833 | 50
out pmt | Monthly payment | $ | p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2