Purchasing a home is one of the most significant financial decisions you will make. This Mortgage Payment Calculator is designed to provide a comprehensive breakdown of your monthly financial obligations, moving beyond just the loan repayment to include the "PITI" components: Principal, Interest, Taxes, and Insurance.
Components of Your Monthly Payment
Principal: The portion of your payment that goes toward paying down the original amount you borrowed.
Interest: The cost of borrowing money, paid to the lender. In the early years of a standard 30-year fixed mortgage, the majority of your payment goes toward interest.
Property Taxes: Assessed by your local government to fund public services. This is usually held in escrow by your lender and paid annually or semi-annually on your behalf.
Homeowners Insurance: Protects your property against damage and liability. Like taxes, this is often bundled into your monthly payment.
HOA Fees: If you buy a condo or a home in a managed community, you may owe Homeowners Association fees. While usually paid directly to the association, including them here gives a true picture of housing affordability.
How Interest Rates Affect Affordability
Even a small fluctuation in interest rates can drastically alter your buying power. For a $300,000 loan, a 1% increase in interest rate can increase your monthly payment by hundreds of dollars and add tens of thousands of dollars to the total cost of the loan over 30 years.
Using This Calculator
Input your expected home price and down payment to determine the loan amount. Adjust the interest rate based on current market trends and your credit score. Don't forget to estimate property taxes (typically 1-2% of home value annually) and insurance to ensure the total monthly payment fits within your budget.
function calculateMortgage() {
// 1. Get Input Values
var price = parseFloat(document.getElementById('homePrice').value);
var downPayment = parseFloat(document.getElementById('downPayment').value);
var termYears = parseFloat(document.getElementById('loanTerm').value);
var annualRate = parseFloat(document.getElementById('interestRate').value);
var annualTax = parseFloat(document.getElementById('propertyTax').value);
var annualInsurance = parseFloat(document.getElementById('homeInsurance').value);
var monthlyHoa = parseFloat(document.getElementById('hoaFees').value);
// 2. Validate Inputs
if (isNaN(price) || isNaN(downPayment) || isNaN(termYears) || isNaN(annualRate)) {
alert("Please enter valid numbers for Home Price, Down Payment, Term, and Interest Rate.");
return;
}
// Handle optional fields if empty
if (isNaN(annualTax)) annualTax = 0;
if (isNaN(annualInsurance)) annualInsurance = 0;
if (isNaN(monthlyHoa)) monthlyHoa = 0;
// 3. Perform Calculations
var loanAmount = price – downPayment;
if (loanAmount <= 0) {
alert("Down payment cannot equal or exceed home price for a mortgage calculation.");
return;
}
var monthlyRate = (annualRate / 100) / 12;
var numberOfPayments = termYears * 12;
var monthlyPrincipalInterest = 0;
// Mortgage Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
if (annualRate === 0) {
monthlyPrincipalInterest = loanAmount / numberOfPayments;
} else {
var mathPower = Math.pow(1 + monthlyRate, numberOfPayments);
monthlyPrincipalInterest = loanAmount * (monthlyRate * mathPower) / (mathPower – 1);
}
var monthlyTax = annualTax / 12;
var monthlyInsurance = annualInsurance / 12;
var totalMonthlyPayment = monthlyPrincipalInterest + monthlyTax + monthlyInsurance + monthlyHoa;
var totalCostOfLoan = (monthlyPrincipalInterest * numberOfPayments);
var totalInterest = totalCostOfLoan – loanAmount;
// 4. Format and Display Results
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 2
});
document.getElementById('resPrincipalInterest').innerText = formatter.format(monthlyPrincipalInterest);
document.getElementById('resTax').innerText = formatter.format(monthlyTax);
document.getElementById('resInsurance').innerText = formatter.format(monthlyInsurance);
document.getElementById('resHoa').innerText = formatter.format(monthlyHoa);
document.getElementById('resTotal').innerText = formatter.format(totalMonthlyPayment);
document.getElementById('resLoanAmount').innerText = formatter.format(loanAmount);
document.getElementById('resTotalInterest').innerText = formatter.format(totalInterest);
// Show the results container
document.getElementById('mpResults').style.display = 'block';
}