Calculate a Personal Loan Payment: Formula and Example

Calculate a personal loan’s monthly payment by entering the amount borrowed, annual percentage rate (APR), and loan term; the calculator uses a fixed-rate, level-payment formula. It returns the estimated monthly payment and total interest, with the payment rounded to the nearest cent.

Formula

The standard fixed-payment formula converts the annual APR to a monthly rate, then calculates the payment that repays principal and interest over the specified number of months:

Payment = P × r ÷ [1 − (1 + r)⁻ⁿ]

• P is the amount borrowed, in dollars.
• r is the monthly interest rate as a decimal: APR ÷ 1,200. For an 8% APR, r = 8 ÷ 1,200.
• n is the number of monthly payments: loan term in years × 12.

The calculator’s first result is the monthly payment, rounded to cents. Its second result estimates total interest as the rounded monthly payment multiplied by the number of months, minus the original principal. Because it uses the rounded payment, the displayed total is an estimate; a lender’s final payment schedule may account for more precise calculations or a different final payment.

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 ÷ 1,200 = 0.0066667.
2. Find the number of payments: 5 × 12 = 60 months.
3. Substitute into the payment formula: $20,000 × 0.0066667 ÷ [1 − (1 + 0.0066667)⁻⁶⁰].
4. The unrounded payment is about $405.53, so the monthly payment rounded to cents is $405.53.
5. Estimate total interest using the rounded payment: $405.53 × 60 − $20,000 = $4,331.80.

Assumptions

• The interest rate stays fixed throughout the term.
• Payments are equal monthly payments, made at regular intervals; the formula treats each payment as occurring at the end of a monthly period.
• Interest compounds monthly using APR ÷ 12.
• The estimate excludes fees, taxes, insurance, and other charges. The calculator has no inputs for these costs.

How to Read the Payment and Interest

The monthly payment is the amount the formula assigns to each scheduled installment. Early in a standard amortizing loan, a larger share of each payment generally covers interest; as the balance falls, more goes toward principal. The total-interest figure estimates the interest paid over all scheduled payments, not the total amount repaid. To estimate the total of payments, add the original principal to the displayed interest, while remembering that rounding and lender-specific terms can change the final amount.

The payment is not necessarily the full monthly cost of borrowing. A lender may disclose fees or other charges separately, and the calculator does not add them to the result. If charges are financed into the loan, the amount borrowed for the calculation should reflect the principal actually being repaid, but the lender’s documents determine how the loan is structured.

What Changes a Personal Loan Payment?

• Loan amount: With the same APR and term, a larger principal produces a larger scheduled payment.
• APR: A higher input APR increases the interest cost and usually raises the payment for a fixed term and amount.
• Term: Spreading principal over more monthly payments often lowers the scheduled payment, but can increase total interest because interest accrues over more time.
• Fees or add-ons: These may affect the amount financed or the overall cost, but are not modelled unless included in the loan amount or entered through a separate calculator.

These are mathematical relationships, not guidance about selecting a loan. Enter the actual figures disclosed by the lender to estimate the payment for a specific offer. The defaults are an example only; they do not describe a current or typical rate, fee, loan limit, or approval standard.

Common Calculation Problems and Limits

A common mistake is entering an APR such as 8 as though it were a decimal rate. This calculator expects a percentage, so enter 8 for 8%; it converts the annual figure to a monthly rate internally. Another mistake is mixing a term in months with a term in years: the input here is years, and the formula multiplies it by 12. Keep the principal in dollars and the APR as an annual percentage.

The formula assumes one fixed rate and equal monthly payments. It does not represent a variable rate, irregular payment dates, skipped payments, late charges, optional payment protection, or extra principal payments. It also does not determine whether a lender will approve an application or what rate or fees will be offered. If an actual disclosure lists a different payment, check its term, payment schedule, financed charges, and rounding conventions rather than assuming the calculation is wrong.

Frequently Asked Questions

How do I calculate a personal loan payment by hand?
Convert APR to a monthly decimal by dividing it by 1,200, convert the term to months, and substitute both values and the principal into the fixed-payment formula above.

Does a longer loan term lower the monthly payment?
For the same principal and APR, a longer term generally spreads repayment across more installments and lowers the scheduled payment. It can also increase total interest because the balance is outstanding for longer.

Is APR the same as the monthly interest rate?
No. APR is entered as an annual percentage. This estimate divides it by 12 to get the monthly rate, using APR ÷ 1,200 to express that rate as a decimal.

Does the payment include personal loan fees?
No. The calculator uses only the amount borrowed, APR, and term. Fees or other charges may be handled separately or affect the amount financed; consult the lender’s disclosure for the actual terms.

Why might my lender’s payment differ from this estimate?
The lender may use different rounding, payment dates, financed charges, or contract terms. Compare the calculator’s assumptions with the figures and schedule in the loan disclosure.

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

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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