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01 Loan payments

Fixed Payment Loan Calculator: Monthly Payment & Interest

Calculator No. 01-4934 · Updated · Formula and assumptions shown below

Monthly payment $405.53
Total interest
$4,331.80
= Monthly payment × loan term × 12 − loan amount
Loan amount
$20,000
Input
Interest rate (APR)
8 %
Input
You enter
Loan amount ($), Interest rate (APR) (%), Loan term (years)
You get
Monthly payment ($), Total interest ($)
Rounding
2 dp

Estimate for education, not financial advice. The result follows from the numbers you enter and the formula shown. It is not a quote or an offer, and it does not include fees, taxes or insurance unless the calculator asks for them. Ask your lender for the exact figures.

A fixed payment loan calculator estimates the equal monthly payment needed to repay a loan over a set term, along with total interest. Enter the amount borrowed, annual percentage rate (APR), and term; the results use monthly payments and a fixed rate.

Formula

The calculator uses the standard fixed-payment amortization formula. It first calculates the payment that makes the loan balance reach zero after the scheduled number of monthly payments:

Payment = round(P × r / (1 − (1 + r)−n), 2)

  • P is the starting loan principal, in dollars.
  • r is the monthly interest rate, calculated as APR ÷ 1200. For an APR of 8%, for example, the monthly rate is 8 ÷ 1200.
  • n is the number of monthly payments, calculated as loan term in years × 12.
  • Payment is the scheduled monthly amount, rounded to the nearest cent.

Total interest is calculated as Payment × n − P. Because this total uses the payment rounded to cents, it reflects the displayed monthly payment. Real loan schedules may adjust the final payment slightly to clear a remaining rounding difference.

Worked Example

Using the calculator’s defaults: principal P = $20,000, APR = 8%, and term = 5 years.

  1. Convert the APR to a monthly rate: r = 8 ÷ 1200 = 0.0066666667.
  2. Convert years to monthly payments: n = 5 × 12 = 60.
  3. Substitute into the payment formula: $20,000 × 0.0066666667 ÷ (1 − (1 + 0.0066666667)−60).
  4. Round the result to cents: monthly payment = $405.53.
  5. Calculate total interest using that rounded payment: $405.53 × 60 − $20,000 = $4,331.80.

Assumptions

  • The interest rate stays fixed for the full term.
  • Payments are equal monthly payments made at the end of each period.
  • Interest accrues monthly at APR divided by 12.
  • The calculation excludes fees, taxes, insurance, PMI, and escrow; none of these are entered as calculator inputs.

How to Use and Read the Results

Enter the amount financed—not necessarily the purchase price—then enter the APR and repayment term. The payment result is the estimated principal-and-interest amount due each month under the stated assumptions. The total-interest result is the interest implied by making that rounded payment for every scheduled month.

For a real estimate, use figures from the lender’s loan disclosure or other documents for the proposed loan. Check whether the quoted APR and term describe the same borrowing arrangement represented by the calculator. If a loan has an upfront charge, a changing rate, or a different payment frequency, this basic formula may not reproduce its schedule.

A fixed payment does not mean the same amount of every payment goes toward principal. At the beginning, more of each payment generally covers interest because the outstanding balance is larger. As the balance falls, the interest portion falls and the principal portion rises. The scheduled total stays level when the assumptions hold.

Why Payment and Interest Change

The payment is determined by the principal, rate, and term together. A larger principal increases the amount being repaid. A higher APR increases the monthly interest charge. A longer term spreads repayment over more months, which can reduce the scheduled monthly payment while increasing the total interest paid over the full schedule. These are mathematical effects, not a recommendation about which loan terms to use.

For example, the calculator’s $20,000, 8%, five-year example has a $405.53 monthly payment and $4,331.80 in calculated interest. A different term or APR would produce a different pair of results; to compare scenarios, change one input at a time and keep the other assumptions consistent.

Common Limits and Mistakes

  • Entering 8 instead of 0.08: Enter APR as a percentage number, such as 8 for 8%, not as a decimal fraction.
  • Confusing term units: The term input is in years. A five-year loan is entered as 5; the formula converts it to 60 months.
  • Treating the payment as the full bill: The result covers scheduled principal and interest only. Costs such as insurance, taxes, fees, or escrow are outside the calculation.
  • Assuming every loan has a fixed rate: A variable-rate loan can have changing payments or interest costs, which this calculator does not project.
  • Overlooking rounding: Payments are rounded to cents. Actual servicing schedules can have a slightly different final payment, especially when payment dates or daily interest calculations differ.

This formula describes a level-payment, fully amortizing loan: each scheduled payment is sufficient, under the assumed rate and timing, to repay principal and interest by the end of the term. It does not model skipped or late payments, extra principal payments, fees added to the balance, balloon payments, or rate changes. To examine those cases, the schedule and calculation need the relevant details.

Frequently Asked Questions

What is a fixed payment loan?
A fixed payment loan has scheduled payments that remain equal under the contract’s applicable payment terms. In a standard fixed-rate amortizing loan, each payment covers interest and repays part of the principal.

Does a fixed payment mean a fixed interest rate?
Not necessarily in every loan arrangement. This calculator assumes the rate remains fixed throughout the term. If a loan’s rate can change, its future payment and interest schedule may differ.

Does this calculator include fees or insurance?
No. It calculates principal-and-interest payments and related interest only. Fees, insurance, taxes, PMI, and escrow are not included because they are not inputs.

Why does a longer loan term usually lower the monthly payment?
The principal is divided across more scheduled payments, so the amount due each month can be lower. Interest continues to accrue over the longer repayment period, so total interest can be higher.

Why might my lender’s payment differ?
The quoted loan may include fees or other financed costs, use different payment dates or interest conventions, or have a different rate or term. Rounding and a final-payment adjustment can also create a small difference. Compare the calculator inputs with the lender’s stated loan terms.

This result is an estimate; 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 | $ | round(p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)), 2) | 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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