Personal Loan Calculator: Payments, Interest and Costs

A personal loan calculator estimates the fixed monthly payment and total interest for a loan when you enter its amount, annual percentage rate (APR), and term. It also shows the total interest across the scheduled payments; it does not determine approval, affordability, or a lender’s exact payoff figure.

Formula

The calculator uses the standard fixed-payment loan formula. It first calculates a level monthly payment, rounded to cents, then subtracts the original principal from the sum of those scheduled payments to estimate total interest.

• p is the loan principal, or amount borrowed, in dollars.
• APR is the annual percentage rate entered as a percentage, such as 8 for 8%.
• r is the monthly rate as a decimal: APR ÷ 1,200.
• n is the number of monthly payments: loan term in years × 12.
• Payment is the monthly payment in dollars: p × r ÷ [1 − (1 + r)⁻ⁿ]. The calculator rounds this payment to the nearest cent.
• Total interest is payment × n − p, using the rounded monthly payment.

The formula assumes equal payments made monthly at a fixed rate. The APR is treated as a nominal annual rate divided by 12 for the calculation; the result is an estimate rather than a lender’s final schedule.

Worked Example

Using the calculator’s default inputs—$20,000 principal, 8% APR, and a five-year term—the calculation has 60 monthly payments and a monthly rate of 0.08 ÷ 12, or approximately 0.0066667.

1. Calculate the payment: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰].
2. The unrounded result is approximately $405.53 per month; rounded to the nearest cent, the displayed payment is $405.53.
3. Calculate interest using the rounded payment: $405.53 × 60 − $20,000 = $4,331.80.

The figures are rounded independently as shown. Multiplying the displayed payment by 60 gives $24,331.80 in scheduled payments, of which $20,000 is principal and $4,331.80 is estimated interest.

Assumptions

• The interest rate remains fixed for the entire term.
• Payments are equal, made monthly, and begin on the assumed schedule.
• Interest is modelled monthly at APR ÷ 12.
• Fees, taxes, insurance, late charges, and other lender-specific costs are not included.

How to Use the Estimate

Enter the amount you expect to borrow, the APR quoted for the loan, and the repayment term. Use the lender’s stated APR and term when available; do not substitute an advertised rate or assume you will receive a particular rate. The calculator accepts APR values from 0.01% to 100% and terms from 0.0833 to 50 years, subject to the input limits.

The monthly payment is the planned amount for principal and interest under the model. Total interest estimates the cost of borrowing over all scheduled payments, excluding the amount repaid as principal. A longer term generally spreads repayment over more installments and changes both the payment and total interest; the exact effect depends on the entered rate and loan amount.

For a comparison, change one input at a time and keep the other assumptions constant. For instance, compare two terms using the same principal and APR to see how the estimated payment and interest differ. This is a mathematical comparison, not a recommendation about which loan or term to choose.

Costs and Comparisons

A personal loan’s quoted payment may not tell the whole cost story. Some offers may include fees or other terms that this calculator cannot represent. Ask the lender which charges are included in its APR and payment quotation, and review the loan disclosure for the amount financed, payment schedule, and total repayment figures. The calculator does not add an origination charge to principal or model a fee deducted from the funds you receive.

When comparing estimates, check that the APR, term, payment frequency, and loan amount refer to the same assumptions. A quoted APR can reflect costs differently from a simple interest rate, while this calculator applies APR ÷ 12 as the monthly rate. If the lender’s schedule includes fees, a different payment date, or another calculation method, its figures can differ.

Common Problems and Limits

• Entering 8 instead of 0.08: The APR field expects a percentage number. Enter 8 for 8%, not 0.08.
• Confusing term units: The term field is in years. Enter 5 for five years, not 60 months.
• Ignoring payment rounding: The displayed payment is rounded to cents, and total interest uses that rounded amount. A lender may adjust a final payment by a small amount to reconcile the balance.
• Treating the estimate as a payoff quote: A payoff amount on a particular date can depend on payment timing and accrued interest, neither of which is captured here.
• Assuming approval or affordability: The calculation uses only the entered figures. It does not assess income, existing debts, eligibility, or a lender’s decision.

The formula also assumes a fully amortizing loan: scheduled payments cover interest and gradually repay principal until the term ends. It does not model variable rates, missed or extra payments, deferment, a balloon payment, or a changing payment schedule. For those situations, a different calculation and the lender’s own schedule may be needed.

Frequently Asked Questions

What does a personal loan calculator calculate?
It estimates a monthly principal-and-interest payment and total interest from the amount borrowed, APR, and term. It does not include unentered fees or predict a lender’s offer.

Is APR the same as the interest rate?
Not necessarily. APR can represent borrowing costs differently from a nominal interest rate, depending on the loan and its terms. This calculator uses the APR you enter as an annual rate divided by 12, so the result may not reproduce a lender’s complete disclosure calculation.

Why is my lender’s monthly payment different?
The lender may use a different APR treatment, include fees, set a different first payment date, or round payments and balances differently. Compare the exact loan amount, APR, term, and payment schedule, then use the lender’s disclosed figures for the actual obligation.

Does the calculator include fees?
No. It calculates principal and interest only. Fees, insurance, taxes, and charges that reduce the cash you receive are not included unless reflected in figures you enter, and the calculator cannot separate them.

Can I use it to work out an early payoff?
No. It assumes scheduled equal monthly payments through the full term. Early payoff estimates require the balance on a specific date and any applicable lender terms; request an exact payoff figure from the lender.

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

Related

• John Deere Financial Loan Calculator: Estimate Payments
• KBZ Bank Loan Calculator: Estimate Monthly Payments
• Interest on Balance Calculator: Formula and Example

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 | $ | round(p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)), 2) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2