The total cost method calculates how much a loan costs over its full repayment term by adding all scheduled payments and subtracting the amount borrowed. Enter the loan principal, annual percentage rate (APR), and term to estimate the monthly payment and total interest; the estimate assumes a fixed rate and regular monthly payments.
Formula
The total cost method, in this calculator, treats the cost of borrowing as the total of the rounded monthly payments minus the original principal. It first calculates a level payment using the standard amortizing-loan formula:
Monthly payment = P × r ÷ [1 − (1 + r)−n]
Total interest = monthly payment × n − P
- P is the amount borrowed, in dollars.
- APR is the annual percentage rate entered as a percentage per year.
- r is the monthly rate, calculated as APR ÷ 1,200. For an 8% APR, r = 0.08 ÷ 12.
- n is the number of monthly payments, calculated as the term in years × 12.
The calculator displays the monthly payment to the nearest cent. Its total-interest calculation uses that displayed, rounded payment multiplied by the scheduled number of months, then subtracts the principal. This makes the result a useful estimate, though an actual lender’s final payment may be adjusted for rounding or account-specific details.
Worked Example
Using the default inputs—$20,000 borrowed, 8% APR, and a five-year term—the calculation has 60 monthly payments and a monthly rate of 0.08 ÷ 12 = 0.0066667.
- Calculate the unrounded payment: $20,000 × 0.0066667 ÷ [1 − (1.0066667)−60] ≈ $405.53.
- Round the monthly payment to cents: $405.53 per month.
- Multiply the rounded payment by 60: $405.53 × 60 = $24,331.80.
- Subtract the original principal: $24,331.80 − $20,000 = $4,331.80 in estimated total interest.
The headline figure is the monthly payment. The second result is the estimated interest cost over the scheduled term; adding it back to the principal gives the estimated total repaid, $24,331.80.
Assumptions
- The APR stays fixed for the full term.
- Payments are equal, made monthly, and paid at the end of each monthly period.
- Interest is treated as compounding monthly at APR ÷ 12.
- The calculation excludes fees, taxes, insurance, PMI, escrow, and any optional or late payments.
- The term is treated as a whole number of monthly payments after multiplying years by 12.
What “Total Cost” Means Here
“Total cost method” can refer to different calculations depending on the context. For a loan-payment estimate, it commonly means totaling the required payments over the term and separating the amount borrowed from the financing cost. This page uses total interest as the borrowing-cost measure; it does not add fees or other charges that are not entered as inputs.
That distinction matters. If two loans have the same principal but different terms, the longer term can have a lower monthly payment while producing more total interest, because interest accrues over more payment periods. The calculator makes that trade-off visible through the payment and interest figures, but it does not determine which arrangement is appropriate for any person.
For example, the worked example estimates $24,331.80 in scheduled payments on a $20,000 principal. The $4,331.80 difference is interest under the stated assumptions—not a complete quote of every amount a borrower might pay. If an application includes an origination charge, a separate monthly fee, or a variable rate, those details are outside this calculation.
When to Use It and How to Read the Result
Use the estimate to understand the basic payment pattern of a fixed-rate, fully amortizing loan, or to check the arithmetic in a quoted payment. Enter the principal rather than the amount you expect to receive after deductions if fees are financed or withheld; the lender’s documents should clarify the amount actually borrowed and how charges are handled.
- Monthly payment: the estimated regular principal-and-interest payment, rounded to cents.
- Total interest: the estimated amount paid above principal across the modeled term.
- Estimated total repaid: monthly payment multiplied by the number of payments; it equals principal plus the displayed interest under this calculation.
APR is entered as a percentage, so enter 8 for 8%, not 0.08. The formula converts it to a monthly decimal rate. Loan term is entered in years; a five-year term means 60 monthly payments. If the APR or term is uncertain, use the actual figures supplied for the scenario you want to examine rather than treating the default values as a quote.
Limits and Common Mistakes
This formula assumes a fixed rate and equal payments that fully repay the loan at the end of the term. It does not model variable-rate changes, irregular payment dates, a balloon payment, interest-only periods, skipped payments, extra principal payments, or a payoff before the scheduled end. Those features can change both the payment schedule and total amount paid.
A common misconception is that APR and interest cost are interchangeable. APR is an annualized rate used here to calculate interest; total interest is a dollar amount over the selected term. Some APR disclosures reflect certain borrowing charges, while this calculator does not separately add fees. Therefore its total-interest result should not be mistaken for a complete comparison of all loan costs.
Rounding also affects the final cents. The formula rounds the monthly payment to two decimal places, then uses that rounded figure for all scheduled payments. A lender may calculate interest daily, apply payments on different dates, or adjust the final payment, so the exact disclosed amount can differ slightly. Enter rates and terms carefully, and use the lender’s itemized figures for charges that are not represented here.
Frequently Asked Questions
What is the total cost method for a loan?
It estimates the amount paid over the loan term and separates the amount borrowed from the cost of borrowing. In this calculator, total interest is scheduled payments minus principal.
Is total cost the same as total interest?
No. Total interest is the estimated financing cost above principal. Total repaid includes both principal and interest; a broader loan cost could also include fees or other charges.
Does a longer loan term lower the total cost?
Not necessarily. A longer term can reduce the scheduled monthly payment, but it also means more periods in which interest may accrue. This calculator shows the resulting estimate for the inputs entered.
Does this calculator include loan fees?
No. It models principal, APR, and term only. Fees, taxes, insurance, PMI, and escrow are excluded unless separately accounted for in the loan figures.
Why might my lender’s payment differ?
The lender may use different payment dates, daily interest calculations, fees, a variable rate, or a final-payment adjustment. Compare the calculator’s assumptions with the lender’s payment schedule and disclosure.
This result is an estimate for educational purposes, and the lender’s disclosure gives the exact figures.
Related
Formula used
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
Each line is one input (in, sel, list) or one result (out: label, unit, formula, decimals). How the calculators work
Method: the standard loan formula for this calculation, fixed rate and monthly compounding unless stated, rounded as each result states. Not financial advice; no lender, rate or product is recommended. See formulas and assumptions, the disclaimer or report an error.
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