Personal Loan Monthly Payment Calculator & Formula

A personal loan monthly payment calculator estimates the fixed payment needed to repay a loan over a chosen term, plus the total interest under the same assumptions. Enter the loan amount, annual percentage rate (APR), and term in years to see an estimated monthly payment and total interest.

Formula

The calculator uses the standard fixed-payment amortization formula. First, it converts the annual APR to a monthly rate and the term in years to a number of monthly payments:

r = APR / 1200
n = years × 12
Monthly payment = round[P × r / (1 − (1 + r)⁻ⁿ), 2]
Total interest = monthly payment × n − P

• P is the amount borrowed, in dollars.
• APR is the annual percentage rate entered as a percentage, such as 8 for 8%.
• r is the monthly interest rate as a decimal.
• n is the number of monthly payments.
• Monthly payment is rounded to the nearest cent before total interest is calculated.

The formula assumes a level payment each month and a fixed rate. APR is divided by 12 to represent a monthly rate; the formula does not separately model a lender’s exact daily accrual method or payment-date conventions.

Worked Example

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

For these inputs, the estimated monthly payment is $405.53 and estimated total interest is $4,331.80. The final payment shown by a lender may differ slightly because actual loan calculations can use more precise rates, specific dates, fees, or a different payment schedule.

Assumptions

• The interest rate remains fixed for the full term.
• Payments are equal and made monthly, with the first payment one month after the loan is issued.
• Interest compounds monthly at APR divided by 12.
• The estimate excludes origination or other fees, taxes, insurance, PMI, and escrow; none of these are inputs in this calculator.

When to Use a Monthly Payment Estimate

This calculation is useful for understanding how the amount borrowed, interest rate, and repayment length affect a level monthly payment. You can enter figures from a lender’s written quote to reproduce a basic payment estimate, or use hypothetical values to see the arithmetic. For an actual quote, obtain the rate, fees, payment schedule, and amount financed directly from the lender; do not treat the default inputs as an offer or a prediction of approval.

Change one input at a time if you want to isolate its effect. For example, holding the loan amount and APR constant while changing the term shows how spreading repayment over more months affects the payment and total interest. A longer term generally means more scheduled payments, so the total-interest figure can rise even when the monthly payment falls. The calculator reports arithmetic only; it does not assess income, expenses, eligibility, or suitability.

How to Read the Results

The monthly payment is the modeled amount applied each month toward interest and principal. At the beginning of a typical amortizing loan, a larger portion of each payment goes toward interest because the balance is higher. As the balance declines, the interest portion usually decreases and more of each level payment reduces principal.

Total interest is the sum implied by the rounded monthly payment across the full number of scheduled payments, less the original principal. It is not the total of all cash paid: adding the loan amount to the displayed interest gives the modeled total paid, before excluded charges. Because each payment is rounded to cents, a real final installment may be adjusted to clear a small remaining balance.

Common Mistakes and Limits

• Entering APR as a decimal: enter 8 for 8%, not 0.08. The calculator performs the percentage conversion.
• Mixing years and months: the term input is in years, and the formula multiplies it by 12. Do not enter 60 to mean five years.
• Assuming the payment includes every charge: the displayed payment excludes fees and other costs unless they are included in the principal or modeled separately.
• Treating an estimate as a quote: the actual amount financed, payment dates, rounding, and contract terms may change the figures.

The calculation requires a positive APR and a positive term. It models a fixed-rate, fully amortizing loan with equal monthly payments; it is not designed for variable rates, irregular payments, deferred interest, balloon payments, or a loan with a separate fee schedule. A fee included in the amount financed can affect the payment because it changes the principal, while a fee paid separately is not represented here.

Frequently Asked Questions

How do I calculate a personal loan monthly payment?
Convert APR to a monthly decimal rate by dividing it by 1,200, convert years to months, and apply 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 modeled payment includes both interest for that period and repayment of principal. The proportions change over time, although the calculated payment stays level under the fixed-rate assumptions.

Why can my lender’s payment differ from this result?
A lender may use a different financed amount, fees, rate precision, payment dates, accrual method, or rounding procedure. Compare the calculator inputs with the figures and schedule in the lender’s disclosure.

Does a longer loan term reduce total interest?
Not necessarily. A longer term can lower the scheduled monthly payment while increasing the number of payments, which may increase total interest under the same rate and principal.

Can I use this calculator for a variable-rate loan?
Not as a full payment forecast. The formula holds APR constant for the entire term, so it cannot account for future rate changes or resulting payment adjustments.

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