Monthly Personal Loan Calculator: Payment and Interest

A monthly personal loan calculator estimates your fixed monthly payment and total interest from the loan amount, annual percentage rate (APR), and term. Enter those three figures to see the payment and estimated interest under a standard fixed-rate repayment formula.

Formula

The standard fixed-payment formula converts the annual APR to a monthly rate and spreads repayment across the full term:

Monthly 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 = 0.08 ÷ 12.
• n is the number of monthly payments: loan term in years × 12.
• APR is entered as a yearly percentage, not a decimal. The calculator uses APR ÷ 12 as the monthly rate.

Total interest is estimated as the monthly payment multiplied by the number of payments, minus the original principal: Total interest = monthly payment × n − P. The payment is displayed to the nearest cent, and the interest calculation uses that displayed payment. Actual lender schedules may differ slightly because of payment dates, rounding practices, fees, or other contract details.

Worked Example

Using the calculator’s default inputs—$20,000 borrowed, 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 monthly payments: 5 × 12 = 60.
3. Apply the fixed-payment formula: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰].
4. Round the monthly payment to cents: $405.53 per month.
5. Calculate estimated interest using the rounded payment: $405.53 × 60 − $20,000 = $4,331.80.

The estimated total of scheduled payments is $24,331.80: $20,000 in principal plus $4,331.80 in interest. The numbers are estimates based on the stated inputs, not a lender’s payment quote.

Assumptions

• The interest rate is fixed for the whole term.
• Payments are equal, made monthly, and timed at the end of each monthly period.
• Interest accrues monthly using APR divided by 12.
• The estimate excludes fees and does not model taxes, insurance, PMI, or escrow. It also assumes no late payments, skipped payments, or extra principal payments.

When to Use the Calculator

Use the estimate to understand how the amount borrowed, APR, and repayment term work together. It can help you compare hypothetical loan structures on the same mathematical basis, or check a payment figure against the basic fixed-rate calculation. Enter the APR and term quoted for the particular loan rather than relying on a general rate or an assumed offer. If the lender provides a fee-inclusive figure or a different payment schedule, that may not match this calculator’s inputs or formula.

Changing one input at a time shows its mathematical effect. A larger principal raises the payment when the rate and term stay constant. A higher APR raises both the payment and total interest. Extending the term generally lowers the scheduled monthly payment but increases the number of payments, which can raise total interest. These are formula outcomes, not a judgment about which loan structure is suitable for anyone.

How to Read the Results

The first output is the estimated amount due each month under the assumptions above. The second is estimated interest across all scheduled payments; it is not the total amount repaid. Add principal to interest to get the estimated total paid. The calculation does not show an amortization table, but in a standard amortizing loan each payment covers interest accrued for that period and reduces the remaining principal. Early payments can therefore include a larger interest portion than later payments.

A monthly payment is not necessarily the entire cost of borrowing. A lender’s disclosure may include an origination fee or other charges, and the fee may be paid separately or handled in another way. Check the lender’s stated amount financed, payment schedule, APR, and total of payments when reviewing actual figures. The calculator cannot infer those contract details from principal, APR, and term alone.

Common Errors and Limits

• Entering APR in the wrong format: enter 8 for 8%, not 0.08. The formula divides the percentage by 1,200 to obtain a monthly decimal rate.
• Mixing years and months: this calculator asks for the term in years and converts it to months. A five-year term means 60 payments, not five.
• Confusing interest with total repayment: total interest excludes the original principal.
• Assuming all personal loans use this schedule: variable rates, irregular payment timing, fees, balloon payments, or other structures require different calculations.
• Expecting exact cents for a real loan: payment dates, daily interest, rounding, and contract terms can cause differences.

The formula assumes a positive APR and a level payment schedule. It does not determine eligibility, lender pricing, fees, or the amount a lender may offer. Use the figures from the lender’s written disclosure for a specific loan, and check whether its APR and payment amount reflect fees or other charges.

Frequently Asked Questions

How do I calculate a monthly personal loan payment?
Convert APR to a monthly decimal by dividing it by 1,200, convert the term to months, then use the fixed-payment formula shown above. This calculator performs those steps and rounds the payment to cents.

Does the monthly payment include interest?
Yes. Each scheduled payment includes interest and repayment of principal under the fixed-rate formula. The interest output is the estimated interest across all payments, not the interest in one month.

Why does a longer loan term reduce the monthly payment?
The principal is divided across more monthly payments. Because interest also accrues during the additional months, a longer term can result in more total interest even when its monthly payment is lower.

Is APR the same as the interest rate?
They are related but not always identical. APR is an annual percentage figure that may reflect certain borrowing costs, depending on the loan and its disclosure. This calculator uses the entered APR as the annual rate in its monthly-payment formula; it does not separately add fees.

Why does my lender’s payment differ from this estimate?
The lender may use different payment dates, rounding, fees, or a repayment structure that does not match the formula’s assumptions. Compare the calculator inputs with the lender’s written payment schedule and disclosure.

This result is an estimate, and 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