APR Total Cost Calculator: Payment and Interest

The APR total cost calculator estimates a fixed-rate loan’s monthly payment and total interest from the loan amount, APR, and term. Enter those three figures to see the scheduled payment and the interest paid if every payment is made on time; it does not add fees or other borrowing costs to the total.

Formula

The calculator uses the standard amortizing-loan payment formula, with the monthly payment rounded to the nearest cent:

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 rate, calculated as APR ÷ 1,200. At an 8% APR, r is 0.0066667, or about 0.6667% per month.
• n is the number of monthly payments, calculated as the term in years × 12.

In the formula, APR is divided by 1,200 because the percentage must first be converted to a decimal and then divided into 12 monthly periods. Total interest is the sum of the rounded scheduled payments minus the original principal. Because payments are rounded to cents, the actual final payment can differ slightly from a perfectly level schedule.

Worked Example

Using the calculator’s default inputs—$20,000 borrowed, 8% APR, and a 5-year term—the calculation is:

1. Convert the APR to a monthly rate: 8 ÷ 1,200 = 0.0066667.
2. Convert the term to payments: 5 × 12 = 60 monthly payments.
3. Substitute into the payment formula: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰] = approximately $405.53 per month after rounding.
4. Calculate total interest using the rounded payment: $405.53 × 60 − $20,000 = $4,331.80.

The displayed outputs are a monthly payment of $405.53 and total interest of $4,331.80, assuming all 60 scheduled payments are made as modeled.

Assumptions

• The rate stays fixed throughout the loan term.
• Payments are equal monthly payments made at the end of each monthly period.
• Interest accrues monthly using the APR divided by 12; the calculator treats APR as a nominal annual rate for this arithmetic.
• The model excludes origination and other fees, taxes, insurance, PMI, escrow, late charges, and any optional products. It also assumes no extra payments, missed payments, or changes to the schedule.

What “Total Cost” Means Here

“Total cost” can refer to different amounts. This calculator reports principal plus modeled interest indirectly: the total of the scheduled payments is the loan amount plus the displayed interest. It does not calculate a complete borrowing cost that includes charges paid upfront or separately. For the default example, the scheduled payments add up to $24,331.80: $20,000 in principal and $4,331.80 in interest.

APR is a rate expressed annually, but the number alone does not tell the calculator every detail of a particular loan agreement. The entered APR is used as the rate for this simplified monthly amortization calculation. If a lender’s quoted APR reflects fees or uses a different payment schedule, its disclosure may show a different payment, finance charge, or total of payments. Use the figures and definitions supplied by the lender when checking a specific offer.

How to Use and Interpret the Results

Enter the amount actually financed, the APR as a percentage, and the term in years. For instance, enter 8 for 8%, not 0.08. The calculator accepts a term from 0.0833 to 50 years and an APR from 0.01% to 100%; these are calculator input limits, not statements about available loan products. The APR must be positive because the payment formula divides by the monthly rate.

• Monthly payment is the fixed principal-and-interest amount implied by the inputs. It is not a full monthly housing or ownership cost.
• Total interest is the estimated interest over the modeled term, calculated from the rounded monthly payment.
• Payment total can be found by adding the principal to total interest, or by multiplying the displayed monthly payment by the number of payments.

A longer term generally spreads repayment across more installments, while the APR and principal also affect the payment and total interest. The calculator does not determine whether a payment fits an individual budget, whether an application will be approved, or which loan terms apply. Obtain the actual APR, amount financed, payment schedule, and any charges from the lender’s documents rather than treating a sample calculation as a quote.

Common Limits and Calculation Mistakes

A frequent input error is typing the APR in decimal form: entering 0.08 means 0.08%, not 8%. Another is entering the number of months in the years field. A 60-month term should be entered as 5 years. Check that the loan amount represents the principal being financed, rather than a purchase price that does not account for a down payment or other adjustments.

This formula is for a fully amortizing loan with regular monthly payments and a fixed rate. It does not model a variable rate, interest-only period, balloon payment, irregular payment dates, daily interest calculations, or a changing balance due to extra payments. If payments are not made according to the assumed schedule, actual interest and payoff timing can differ. Rounding each payment to cents also means the lender may adjust the final payment to clear a small remaining balance.

For a fuller cost picture, compare the calculator’s assumptions with the lender’s written disclosure and separately account for charges that are not included here. This estimate is for educational arithmetic, not financial advice; the lender’s disclosure gives the exact figures.

Frequently Asked Questions

Does APR include loan fees in this calculator?
No. The input APR is used in the monthly payment formula, but fees are not separately entered or added to the total interest. Check the lender’s disclosure to see how its quoted APR and charges are presented.

Is total interest the same as total repayment?
No. Total interest is the amount above the principal in this model. Add the borrowed amount to the interest to get the total of scheduled payments.

Why is the result different from a lender’s payment quote?
The quote may reflect fees included in the amount financed, a different rate or term, payment timing, rounding, or loan features this calculator does not model. Compare the inputs and the assumptions with the lender’s figures.

Can I use this calculator for a variable-rate loan?
Not accurately over the entire term. The calculation assumes one fixed APR throughout. A variable rate can change, so future payments and total interest may differ.

Does this include taxes, insurance, or escrow?
No. The outputs cover modeled principal and interest only. Taxes, insurance, PMI, escrow, and other charges are not included.

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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