Calculate your estimated monthly loan payment quickly and easily.
Your Estimated Monthly Payment:
$0.00
Understanding Your Monthly Loan Payment
Calculating your monthly loan payment is a crucial step when considering any type of loan, whether it's a mortgage, auto loan, personal loan, or student loan. The monthly payment is determined by three primary factors: the total loan amount (principal), the annual interest rate, and the loan term (the duration over which you'll repay the loan).
The Formula Behind the Calculation
The standard formula used to calculate the fixed monthly payment (M) for an amortizing loan is:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
Where:
M = Your total monthly mortgage payment
P = The principal loan amount (the total amount you borrow)
i = Your monthly interest rate. This is calculated by dividing the annual interest rate by 12 (e.g., 5.5% annual rate / 12 months = 0.055 / 12 ≈ 0.004583)
n = The total number of payments over the loan's lifetime (the loan term in months). For example, a 30-year mortgage has 30 * 12 = 360 payments.
How This Calculator Works
Our calculator takes your inputs for the Loan Amount, Annual Interest Rate, and Loan Term (in Months). It then applies the formula above:
It converts the annual interest rate into a monthly interest rate by dividing it by 100 (to get a decimal) and then by 12.
It calculates the total number of payments by using the provided loan term in months.
It plugs these values, along with the loan amount, into the standard loan payment formula.
The result is your estimated fixed monthly payment (principal and interest portion only).
Note: This calculator provides an estimate for the principal and interest portion of your loan payment. For mortgages, additional costs like property taxes, homeowner's insurance, and private mortgage insurance (PMI) may increase your total monthly housing expense.
Use Cases
This calculator is useful for:
Budgeting: Estimate how much a new loan will cost you each month.
Loan Comparison: Compare offers from different lenders with varying interest rates and terms.
Financial Planning: Determine how much you can afford to borrow based on your desired monthly payment.
Debt Management: Understand the repayment structure of existing loans.
function calculateMonthlyPayment() {
var loanAmount = parseFloat(document.getElementById("loanAmount").value);
var annualInterestRate = parseFloat(document.getElementById("annualInterestRate").value);
var loanTermMonths = parseInt(document.getElementById("loanTermMonths").value);
var errorMessageDiv = document.getElementById("errorMessage");
var monthlyPaymentDiv = document.getElementById("monthlyPayment");
errorMessageDiv.textContent = ""; // Clear previous error messages
if (isNaN(loanAmount) || isNaN(annualInterestRate) || isNaN(loanTermMonths)) {
errorMessageDiv.textContent = "Please enter valid numbers for all fields.";
monthlyPaymentDiv.textContent = "$0.00";
return;
}
if (loanAmount <= 0 || annualInterestRate < 0 || loanTermMonths <= 0) {
errorMessageDiv.textContent = "Loan amount and term must be positive. Interest rate cannot be negative.";
monthlyPaymentDiv.textContent = "$0.00";
return;
}
var monthlyInterestRate = (annualInterestRate / 100) / 12;
var numerator = loanAmount * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, loanTermMonths));
var denominator = Math.pow(1 + monthlyInterestRate, loanTermMonths) – 1;
if (denominator === 0) { // Avoid division by zero if monthlyInterestRate is 0
var monthlyPayment = loanAmount / loanTermMonths;
} else {
var monthlyPayment = numerator / denominator;
}
monthlyPaymentDiv.textContent = "$" + monthlyPayment.toFixed(2);
}