The mortgage payment calculator helps you estimate your monthly principal and interest payment for a home loan.
This calculation is crucial for budgeting and understanding the long-term costs of homeownership.
The most common formula used for this calculation is the annuity formula, which determines the fixed periodic payment.
How the Calculation Works
The monthly mortgage payment (M) is calculated using the following formula:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
Where:
P = Principal loan amount (the total amount borrowed)
i = Monthly interest rate (annual interest rate divided by 12)
n = Total number of payments (loan term in years multiplied by 12)
Example Calculation:
Let's say you want to borrow $300,000 (P) with an annual interest rate of 3.5% and a loan term of 30 years.
P = $300,000
Annual Interest Rate = 3.5%
Loan Term = 30 years
First, we need to calculate the monthly interest rate (i) and the total number of payments (n):
This means your estimated monthly principal and interest payment would be approximately $1,348.05.
Important Considerations:
This calculator provides an estimate for the principal and interest portion of your mortgage payment only. It does not include:
Property Taxes
Homeowner's Insurance (HOI)
Private Mortgage Insurance (PMI) (if applicable)
Homeowner Association (HOA) Fees
These additional costs, often referred to as PITI (Principal, Interest, Taxes, Insurance), can significantly increase your total monthly housing expense. Always consult with a mortgage lender for a precise loan estimate.
function calculateMortgage() {
var loanAmount = parseFloat(document.getElementById("loanAmount").value);
var annualInterestRate = parseFloat(document.getElementById("annualInterestRate").value);
var loanTerm = parseFloat(document.getElementById("loanTerm").value);
var resultDisplay = document.getElementById("result-value");
resultDisplay.textContent = "$0.00"; // Reset to default
if (isNaN(loanAmount) || isNaN(annualInterestRate) || isNaN(loanTerm) ||
loanAmount <= 0 || annualInterestRate < 0 || loanTerm <= 0) {
alert("Please enter valid positive numbers for all fields.");
return;
}
// Calculate monthly interest rate
var monthlyInterestRate = annualInterestRate / 100 / 12;
// Calculate total number of payments
var numberOfPayments = loanTerm * 12;
// Calculate monthly payment using the annuity formula
var monthlyPayment;
if (monthlyInterestRate === 0) { // Handle case of 0% interest rate
monthlyPayment = loanAmount / numberOfPayments;
} else {
monthlyPayment = loanAmount * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1);
}
// Format the result to two decimal places
resultDisplay.textContent = "$" + monthlyPayment.toFixed(2);
}