Estimate your monthly house payment including principal and interest.
Estimated Monthly Payment
$0.00
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Understanding Your Mortgage Payment
Buying a home is one of the most significant financial decisions you will ever make. Using a mortgage payment calculator helps you understand the long-term commitment and ensures that your dream home fits within your monthly budget.
How the Mortgage Calculation Works
The monthly payment is calculated using the standard amortization formula. This formula determines the fixed amount you pay each month to ensure the loan is paid off exactly at the end of the term. The math involves:
Principal (P): The total amount borrowed (Home Price minus Down Payment).
Monthly Interest Rate (i): The annual interest rate divided by 12 months.
Number of Payments (n): The number of years multiplied by 12.
Example Calculation
If you purchase a home for $400,000 with a 20% down payment ($80,000), you are financing $320,000. At a 6.5% interest rate over a 30-year term:
Monthly Interest Rate: 0.065 / 12 = 0.005416
Number of Months: 30 * 12 = 360
Using the formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
Result: Your monthly principal and interest payment would be $2,022.62.
Factors That Influence Your Payment
Several variables can change your monthly obligation:
Down Payment: A larger down payment reduces the principal amount, which lowers your monthly payment and reduces total interest paid.
Interest Rates: Even a 0.5% difference in your interest rate can result in tens of thousands of dollars in savings over the life of the loan.
Loan Term: A 15-year mortgage usually has a lower interest rate but higher monthly payments compared to a 30-year mortgage, though you pay significantly less interest overall.
Taxes and Insurance: Remember that this calculator focuses on Principal and Interest (P&I). Your actual bank payment will likely include Property Taxes, Homeowners Insurance, and potentially Private Mortgage Insurance (PMI) if your down payment is less than 20%.
function calculateMortgage() {
var homePrice = parseFloat(document.getElementById("homePrice").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var annualRate = parseFloat(document.getElementById("interestRate").value);
var loanTerm = parseFloat(document.getElementById("loanTerm").value);
if (isNaN(homePrice) || isNaN(downPayment) || isNaN(annualRate) || isNaN(loanTerm)) {
alert("Please enter valid numerical values in all fields.");
return;
}
var principal = homePrice – downPayment;
if (principal <= 0) {
document.getElementById("monthlyPayment").innerHTML = "$0.00";
document.getElementById("totalInterestDisplay").innerHTML = "Down payment exceeds home price.";
return;
}
var monthlyRate = (annualRate / 100) / 12;
var numberOfPayments = loanTerm * 12;
var monthlyPayment;
// Handle 0% interest case
if (monthlyRate === 0) {
monthlyPayment = principal / numberOfPayments;
} else {
var x = Math.pow(1 + monthlyRate, numberOfPayments);
monthlyPayment = (principal * x * monthlyRate) / (x – 1);
}
var totalCost = monthlyPayment * numberOfPayments;
var totalInterest = totalCost – principal;
document.getElementById("monthlyPayment").innerHTML = "$" + monthlyPayment.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("totalInterestDisplay").innerHTML =
"Total Principal: $" + principal.toLocaleString() + " | " +
"Total Interest: $" + totalInterest.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
}
// Run initial calculation on load
window.onload = function() {
calculateMortgage();
};