Please enter valid positive numbers for all fields.
Principal & Interest:
Monthly Property Tax:
Monthly Insurance:
Total Monthly Payment:
function calculateMortgage() {
// Get Input Values
var price = parseFloat(document.getElementById('mc-home-price').value);
var downPayment = parseFloat(document.getElementById('mc-down-payment').value);
var rate = parseFloat(document.getElementById('mc-interest-rate').value);
var termYears = parseInt(document.getElementById('mc-loan-term').value);
var annualTax = parseFloat(document.getElementById('mc-property-tax').value);
var annualInsurance = parseFloat(document.getElementById('mc-home-insurance').value);
var errorDiv = document.getElementById('mc-error');
var resultDiv = document.getElementById('mc-results');
// Validation
if (isNaN(price) || isNaN(downPayment) || isNaN(rate) || isNaN(annualTax) || isNaN(annualInsurance)) {
errorDiv.style.display = 'block';
resultDiv.style.display = 'none';
return;
}
// Logic
errorDiv.style.display = 'none';
var principal = price – downPayment;
var monthlyRate = rate / 100 / 12;
var numberOfPayments = termYears * 12;
// Principal & Interest Calculation
var monthlyPrincipalInterest = 0;
if (rate === 0) {
monthlyPrincipalInterest = principal / numberOfPayments;
} else {
monthlyPrincipalInterest = principal * (monthlyRate * Math.pow(1 + monthlyRate, numberOfPayments)) / (Math.pow(1 + monthlyRate, numberOfPayments) – 1);
}
// Tax and Insurance logic
var monthlyTax = annualTax / 12;
var monthlyInsurance = annualInsurance / 12;
var totalMonthlyPayment = monthlyPrincipalInterest + monthlyTax + monthlyInsurance;
// Display Results
document.getElementById('mc-res-principal').innerText = '$' + monthlyPrincipalInterest.toFixed(2);
document.getElementById('mc-res-tax').innerText = '$' + monthlyTax.toFixed(2);
document.getElementById('mc-res-insurance').innerText = '$' + monthlyInsurance.toFixed(2);
document.getElementById('mc-res-total').innerText = '$' + totalMonthlyPayment.toFixed(2);
resultDiv.style.display = 'block';
}
How to Calculate Your Mortgage Payments
Understanding your monthly mortgage obligation is the first step in the home buying process. This Mortgage Payment Calculator is designed to give you a comprehensive view of your potential financial commitment, going beyond simple principal and interest to include critical escrow items like property taxes and homeowners insurance.
Breaking Down the PITI
In the real estate world, your monthly payment is often referred to as PITI. Here is what that acronym stands for and how each component affects your wallet:
Principal: The portion of your payment that goes directly toward paying down the loan balance ($350,000 home price minus your down payment).
Interest: The cost of borrowing money from the lender. In the early years of a mortgage, a higher percentage of your payment goes toward interest.
Taxes: Property taxes assessed by your local government. These are usually collected by the lender in monthly installments and held in an escrow account.
Insurance: Homeowners insurance protects your property against damage. Like taxes, this is typically paid monthly into escrow.
The Mortgage Formula Explained
While this calculator handles the math for you immediately, understanding the underlying formula can be helpful. The standard calculation for a fixed-rate mortgage is:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
Where:
M = Total monthly payment (Principal + Interest)
P = Principal loan amount
i = Monthly interest rate (Annual rate / 12)
n = Number of months in the loan term
Factors That Impact Your Payment
Several variables can significantly change your monthly outcome:
Down Payment: A larger down payment reduces your principal loan amount, which lowers your monthly payment and the total interest paid over the life of the loan.
Interest Rate: Even a 0.5% difference in interest rates can save (or cost) you tens of thousands of dollars over a 30-year term.
Loan Term: A 15-year term will have higher monthly payments than a 30-year term, but you will pay significantly less interest total.
Why Taxes and Insurance Matter
Many simple mortgage calculators omit property taxes and insurance, leading to "payment shock" when the actual bill arrives. Depending on your location, taxes and insurance can add $300 to $1,000+ to your monthly bill. This tool allows you to input these annual costs to derive a true Total Monthly Payment estimate.