This loan payment calculator estimates the equal payment for a fixed-rate, fully amortizing loan. Enter the loan amount, annual rate, term, and monthly, biweekly, or weekly frequency to see a modeled payment, total interest, and a period-by-period schedule. The results use simplified fixed-rate assumptions and may differ from a lender's payment schedule.
Use the estimate to compare possible loan amounts, rates, and terms before reviewing an actual offer. It does not account for taxes, insurance, other lender fees, or rate changes. An entered origination fee is added to the modeled loan amount.
The Building Blocks of an Installment Loan Payment
For a fixed-rate installment loan, the payment is calculated from the financed amount, periodic rate, and number of payments. This tool uses a standard amortization formula, then walks the balance in cents so the final payment can account for rounding.
Principal Borrowed, Contract Interest Rate, and Repayment Term
Every standard installment loan is governed by three primary contractual parameters:
- Loan amount: The amount entered before the optional fee. If you enter an origination fee, the calculator adds it to this amount to determine the modeled principal.
- Annual interest rate: The fixed nominal annual rate used in the estimate. For each selected frequency, the calculator divides it by 12, 26, or 52 to obtain the periodic rate.
- Term: The loan duration entered in months. For monthly payments, the payment count equals the term; for biweekly or weekly payments, the tool converts months to an approximate number of periods.
How Payment Frequencies Affect the Repayment Cycle
Choose one of the frequencies the calculator supports. The period count is a mathematical conversion of the term, not a dated calendar or a lender's billing arrangement:
- Monthly: Uses 12 periods per year and one payment per entered month of term.
- Biweekly: Uses 26 periods per year; the period count is rounded from the entered term in months.
- Weekly: Uses 52 periods per year; the period count is rounded from the entered term in months.
These options do not model specific payment dates, lender servicing rules, or an accelerated plan that adds a thirteenth monthly payment. A lender may calculate interest and schedule due dates differently.
The Universal Amortization Formula Explained
The standard fixed-payment formula estimates a level payment spread across a fixed number of periods. The calculator rounds payments and balances to cents; it adjusts the final payment to clear the remaining modeled balance.
The Standard Installment Formula
The periodic payment M is expressed mathematically as:
M = P * [ r(1 + r)^n ] / [ (1 + r)^n - 1 ]
Where:
- M: Fixed periodic payment per billing installment.
- P: Total principal amount financed.
- r: Periodic interest rate (nominal annual interest rate expressed as a decimal divided by payment cycles per year).
- n: Total number of scheduled payments across the full term.
Step-by-Step Breakdown of Periodic Rate and Compounding Cycles
To demonstrate how this equation operates in practice, consider a $20,000 loan at a 7.00% annual interest rate over a 60-month term with monthly installments:
- Convert Annual Rate to Periodic Rate: Divide 7.00% by 100 to get 0.07, then divide by 12 monthly periods per year: r = 0.07 / 12 = 0.00583333.
- Calculate Total Payments: For a 5-year loan paid monthly, n = 60.
- Compute Compounding Factor: (1 + 0.00583333)^60 = 1.417625.
- Evaluate the Equation:
Numerator: 20,000 * (0.00583333 * 1.417625) = 20,000 * 0.00826948 = 165.3896.
Denominator: 1.417625 - 1 = 0.417625.
Payment: 165.3896 / 0.417625 = 396.025..., which rounds to $396.03 per month.
How Loan Terms Shape Your Financial Reality
Selecting a repayment term involves navigating a fundamental trade-off between monthly budgeting comfort and long-term borrowing costs.
The Monthly Payment vs Total Interest Paradox
A longer term generally lowers the modeled payment by spreading repayment over more periods, but usually increases total interest when the rate and principal stay the same. Compare both figures against your budget and the actual loan terms.
Evaluating 24, 36, 48, 60, and 72-Month Repayment Schedules
The table below compares monthly payments for a $20,000 installment loan at 7.00% annual interest across common consumer repayment durations:
| Loan Duration | Monthly Payment | Total Interest Paid | Total Amount Repaid | Interest Cost vs 24-Mo Baseline |
|---|---|---|---|---|
| 24 Months (2 Years) | $895.46 | $1,490.85 | $21,490.85 | Baseline cost |
| 36 Months (3 Years) | $617.55 | $2,231.48 | $22,231.48 | +$740.63 (+49.7%) |
| 48 Months (4 Years) | $478.93 | $2,988.36 | $22,988.36 | +$1,497.51 (+100.4%) |
| 60 Months (5 Years) | $396.03 | $3,761.40 | $23,761.40 | +$2,270.55 (+152.3%) |
| 72 Months (6 Years) | $340.99 | $4,550.38 | $24,550.38 | +$3,059.53 (+205.2%) |
In this example, extending the term from 24 to 72 months lowers the monthly payment by $554.47, while modeled interest rises from $1,490.85 to $4,550.38. These are estimates for the stated amount, rate, and monthly frequency; changing the inputs changes the comparison.
Understanding Total Borrowing Cost Beyond the Monthly Note
Evaluating an installment debt requires assessing the total cumulative repayment rather than evaluating the monthly payment in isolation.
Financed Principal vs Cumulative Financing Charges
When you take out an installment loan, your total out-of-pocket obligation equals the sum of all scheduled periodic installments:
Total Interest = Total Payments - Financed Amount
The financed amount includes the loan amount entered plus any optional origination fee.
For the 60-month $20,000 example at 7.00% with no fee, the estimate shows $23,761.40 total paid and $3,761.40 total interest. The calculator carries payments and balances in cents and adjusts the final scheduled payment to clear the remaining modeled balance, so the total is not always exactly the displayed regular payment multiplied by the number of periods.
What This Calculator Assumes: When Terms Differ
This is a fixed-rate amortization estimate, not a quote or a model of every loan contract. Actual payment amounts can differ because of lender-specific rules, payment dates, fees, or rate changes.
Fixed-Rate Fully Amortizing Notes vs Interest-Only Periods
This calculator assumes a fully amortizing fixed-rate structure, where every scheduled payment reduces principal. It does not model:
- Interest-Only Loans: Where payments cover only accrued interest for an initial introductory period (e.g., 5 to 10 years), leaving the entire original principal balance intact.
- Balloon Notes: Where small periodic payments leave a substantial lump-sum balance due on the final contract maturity date.
- Variable-Rate Debt: Where contract interest rates fluctuate with benchmark indexes (such as the SOFR or Prime Rate), altering payment amounts upon each reset date.
How the Optional Origination Fee Is Modeled
Enter the fee as a dollar amount. The calculator adds it to the loan amount before calculating the payment. For example, a $10,000 loan amount with a $500 fee produces a modeled financed amount of $10,500. It does not model a fee deducted from proceeds, calculate a fee as a percentage, or determine which charges count toward APR. Check an actual offer for its fee treatment and amount you will receive.
Because the fee is financed, it compounds. On a $20,000 loan at 7.00% over 60 months with no fee, the estimate shows a $396.03 payment, $3,761.40 of interest, and $23,761.40 total repaid. Enter a $500 financed fee and the modeled principal becomes $20,500: the payment rises to $405.93, interest to $3,855.32, and total repaid to $24,355.32 — the fee itself plus $93.92 of extra interest, and $9.90 more per month.
Related Tools
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Because the inputs are generic, the same screen prices a car loan, an auto refinance balance, a mortgage estimate, student borrowing, or any other amortized loan; the term and rate drive the result, not the label on the loan. Output is a payment schedule, not a graph, and there is no extra-payment input, so an early-payoff question belongs in the Loan Payoff Calculator once a balance exists. Monthly, biweekly, and weekly payment frequencies are supported, and the schedule recasts itself at the cadence you pick.
Last verified: October 2026. Calculator figures are outputs for the inputs entered; they are not live quotes, current rates, or an offer.