Monthly Loan Payment Calculator and Formula

This calculator estimates the fixed monthly payment needed to repay a $20,000 loan over five years at an 8% annual percentage rate (APR). Enter the loan amount, APR, and term to see the estimated monthly payment and total interest under the stated assumptions.

Formula

The fixed monthly payment is calculated using the standard amortizing-loan payment formula:

Payment = P × r ÷ [1 − (1 + r)⁻ⁿ]

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

Total interest in this calculator is estimated as the rounded monthly payment multiplied by the number of payments, minus the original loan amount: interest = payment × n − P. Because the payment is rounded to cents, the final payment on a real loan may differ slightly from the regular payment to bring the balance to exactly zero.

Worked Example

Using the calculator’s default inputs: loan amount P = $20,000, APR = 8%, and term = 5 years.

1. Convert the APR to a monthly decimal rate: r = 8 ÷ 1,200 = 0.0066667.
2. Convert the term to payments: n = 5 × 12 = 60.
3. Substitute into the formula: payment = 20,000 × 0.0066667 ÷ [1 − (1 + 0.0066667)⁻⁶⁰].
4. The unrounded result is about $405.53 per month; rounded to cents, the monthly payment is $405.53.
5. Estimated total interest = $405.53 × 60 − $20,000 = $4,331.80.

Assumptions

• The interest rate remains fixed for the entire repayment term.
• Payments are equal, made monthly, and treated as occurring at the end of each monthly period.
• Interest is modelled monthly using APR ÷ 12, with no separate daily-interest calculation.
• Fees, taxes, insurance, PMI, escrow, and other charges are not included.
• The displayed total interest uses the rounded monthly payment for every scheduled month; a lender’s final payment may be adjusted.

What Determines the Monthly Payment?

The payment depends on the amount borrowed, the interest rate, and the repayment period. A larger principal generally increases the payment. At the same principal and term, a higher rate also increases it. Extending the term spreads repayment across more months, which usually lowers each scheduled payment while increasing the total interest calculated over the full term.

For example, the same $20,000 balance at the same APR would have a different monthly payment if repaid over three years rather than five. The shorter schedule requires the balance to be repaid sooner, so each payment is higher; fewer payment periods generally mean less total interest. Actual loan terms, fees, and payment schedules depend on the lender’s offer, so use the figures supplied for the specific loan rather than assuming the example applies.

How to Use and Read the Estimate

Enter the principal you expect to borrow, the APR as a percentage per year, and the term in years. The first result is the scheduled monthly principal-and-interest payment. The second result estimates interest paid across all scheduled payments, excluding repayment of the principal itself.

Use the monthly figure as a loan-payment estimate, not as a complete monthly housing or ownership cost. For a mortgage, for instance, taxes, insurance, possible mortgage insurance, and escrow arrangements can affect the amount billed or needed each month, but they are not part of this calculation. Similar extra charges may apply to other types of borrowing.

The APR should be the rate that applies to the loan calculation, not a monthly rate. If a lender provides a different periodic rate or a detailed repayment schedule, check which figure is appropriate for comparison and enter the APR as requested here. The calculation does not determine eligibility, approval, or a personal budget.

Common Mistakes and Formula Limits

• Entering 8 instead of 0.08: Enter 8 for an 8% APR. The calculator converts the percentage to a monthly decimal rate itself.
• Mixing years and months: The term field is in years. A five-year term is converted to 60 monthly payments.
• Confusing payment with total cost: The monthly result excludes charges not represented by the inputs. Read the lender’s documents for the complete payment and repayment schedule.
• Assuming every loan has level payments: This formula models a fixed-rate loan with equal monthly payments. Variable rates, interest-only periods, balloon payments, irregular payment dates, and fees added to the balance can produce different results.
• Expecting exact lender figures: Rounding, payment timing, and lender-specific calculations can change the last payment or total. Use the lender’s disclosure for contractual figures.

The formula is useful for estimating a standard amortizing loan when its assumptions match the loan structure. It does not model changes in the rate or payment, nor does it include charges that are not entered. For a precise schedule, compare the calculator’s assumptions with the repayment terms provided by the lender.

Frequently Asked Questions

How do I calculate a monthly loan payment?
Convert APR to a monthly decimal rate by dividing the percentage by 1,200, convert years to months, then use the fixed-payment formula shown above. The calculator performs these steps for you.

Does the monthly payment include interest?
Yes. Each scheduled payment in this model includes principal and interest. The share going to interest is generally larger earlier in a standard amortizing schedule, while the share paying down principal grows over time.

Is APR the same as the monthly interest rate?
No. APR is entered as a yearly percentage. This calculator divides it by 12 to obtain a monthly rate, or equivalently by 1,200 to convert a percentage into a monthly decimal.

Why might my lender’s payment be different?
The lender may use different payment dates, rounding, fees, a variable rate, or other loan terms. This estimate also excludes taxes, insurance, and other charges. Check the lender’s payment schedule and disclosure for the exact figures.

Does a longer loan term lower the payment?
For the same principal and rate under this formula, a longer term generally lowers the scheduled monthly payment because repayment is spread over more months. It also usually raises the total interest calculated across the full schedule.

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

Related

• GPF Final Payment Status: How to Check and What It Means
• Group D Payment Last Date: Check the Official Notice
• GIS Payment Amount: How Much Do You Receive?

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