Total Loan Cost Calculator: Payment, Interest and Total

This calculator estimates the total amount paid on a fixed-rate loan by adding the loan principal to the interest paid over the term. Enter the amount borrowed, annual APR and term in years to see the monthly payment and total interest; the total cost is the principal plus that interest.

Formula

The calculator uses the standard fixed-payment loan formula. It first finds a monthly payment, rounds that payment to the nearest cent, then multiplies it by the number of monthly payments to find the amount repaid. Total interest is the amount repaid minus the original principal; total loan cost is principal plus interest.

• Monthly payment: M = round(P × r ÷ [1 − (1 + r)⁻ⁿ], 2)
• Monthly rate: r = APR ÷ 1,200
• Number of payments: n = years × 12
• Total interest: I = M × n − P
• Total loan cost: C = P + I

P is the amount borrowed in dollars, APR is the annual percentage rate entered as a percentage, r is the monthly rate as a decimal, n is the number of monthly payments, M is the monthly payment in dollars, I is total interest in dollars, and C is total loan cost in dollars. The APR is divided by 1,200 because it is converted from a percentage per year to a decimal per month.

Worked Example

Using the calculator’s defaults—$20,000 borrowed, 8% APR and a five-year term—the number of payments is 5 × 12 = 60, and the monthly rate is 8 ÷ 1,200 = 0.0066667.

1. Monthly payment before cent rounding: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰] ≈ $405.53.
2. Monthly payment rounded to cents: $405.53.
3. Total paid using that rounded payment: $405.53 × 60 = $24,331.80.
4. Total interest: $24,331.80 − $20,000 = $4,331.80.
5. Total loan cost: $20,000 + $4,331.80 = $24,331.80.

Because the payment is rounded to cents before totals are calculated, the displayed total reflects 60 payments of $405.53. A lender’s actual final payment may be adjusted slightly to bring the balance exactly to zero.

Assumptions

• The interest rate stays fixed for the entire term.
• Payments are equal, made monthly, and begin one month after the loan is issued.
• Interest compounds monthly using APR divided by 12.
• The estimate excludes origination or other fees, taxes, insurance, PMI and escrow because none are calculator inputs.

What Total Loan Cost Includes

For this calculation, total loan cost means the principal borrowed plus the modeled interest paid. It is not necessarily the complete cost of obtaining or maintaining a loan. Charges outside the principal-and-interest schedule can raise the amount paid, while a fee paid separately may not appear in the monthly payment. Check the lender’s written disclosure for the costs and payment schedule applicable to a specific offer.

The principal is the money provided to the borrower, not the interest charged for using it. For a fully amortizing loan, each scheduled payment covers interest accrued for the period and reduces the remaining principal. Early in the schedule, a larger share of a level payment generally goes toward interest; later, more goes toward principal. The payment amount can stay level even as that split changes.

How to Use the Result

The headline total is an estimate of all scheduled principal and interest payments over the entered term. The interest output isolates the financing charge in the model, while the monthly payment helps show the schedule’s regular cash outflow. For example, a total of $24,331.80 on a $20,000 principal means $4,331.80 is modeled interest, not an additional amount borrowed.

To make a useful estimate, enter the loan amount, APR and term from the same loan scenario. An advertised rate may not be the APR, and an introductory or variable rate may not remain constant; a fixed-rate calculation cannot represent later rate changes. If the lender provides a payment quote, compare the inputs and included charges before treating the calculator’s result as an equivalent figure.

What Changes the Total

• Borrowed amount: A larger principal generally produces a larger payment and more interest when APR and term are unchanged.
• APR: A higher input rate increases the modeled payment and interest; use the rate quoted for the loan, not a guess.
• Term: A longer term means more monthly payments. It can lower the scheduled payment while increasing the total interest, depending on the same principal and rate.
• Fees and add-ons: Upfront fees, insurance, taxes or other charges are not included unless financed into the principal or entered separately in a different calculation.
• Payment rounding: The calculator rounds each scheduled payment to cents and uses that rounded amount in its totals. Actual schedules can differ by a small amount because of lender rounding and final-payment adjustments.

Limits and Common Misunderstandings

A common misconception is that “total cost” always means every dollar connected with borrowing. Here it means principal plus interest under the stated assumptions. It does not include non-loan expenses, nor does it estimate the effect of making extra payments, skipping or deferring payments, refinancing, or changing rates. Those events alter the payment schedule and need a different calculation.

The formula also assumes regular monthly periods and a fixed APR. Actual interest accrual can depend on the loan contract’s timing and calculation method. If a loan has variable rates, irregular payment dates, a balloon payment, or fees rolled into the balance, this simple estimate may not match its disclosure. Use the lender’s stated figures for a precise contractual schedule and verify that the APR and term entered are expressed in the same way as the quote.

Frequently Asked Questions

How do I calculate the total cost of a loan?
For a fixed-rate, fully amortizing loan, calculate the monthly payment, multiply it by the number of monthly payments to get total paid, then subtract the principal for interest. Total cost in this calculator is principal plus that interest.

Does total loan cost include fees?
No. This calculator includes principal and modeled interest only. Add fees or other charges separately when assessing the full amount paid, and consult the lender’s disclosure for charges tied to a specific loan.

Why is the total paid more than the amount borrowed?
The difference is interest charged over time. In this estimate, total paid equals the rounded monthly payment multiplied by the number of payments.

Can a longer loan term reduce total cost?
Not necessarily. A longer term can reduce the scheduled monthly payment but usually adds more payment periods, which can increase total interest when the principal and APR stay the same.

Why might my lender’s figure differ?
The quoted schedule may include fees, use different payment dates or rounding, or have terms not represented here. Variable rates, additional payments and a final-payment adjustment also change the result.

This result is an estimate for educational purposes, not financial advice; 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
out tot | Total loan cost | $ | p + int | 2