Loan Summary:
Loan Amount:
Total Interest Paid (Over Full Term):
Total Cost of Loan:
How to Calculate Your Mortgage Payments
Understanding your monthly mortgage payment is the first step in determining "how much house" you can afford. While the sticker price of a home is important, the monthly obligation is what affects your daily budget. This calculator helps you break down the four key components of a mortgage payment: Principal, Interest, Taxes, and Insurance (often abbreviated as PITI).
The 4 Components of a Mortgage Payment (PITI)
Principal: The portion of your payment that goes toward paying down the loan balance. In the early years of a mortgage, this amount is small, but it grows over time.
Interest: The cost of borrowing money. This is paid to the lender. With an amortization schedule, you pay more interest at the beginning of the loan term.
Taxes: Property taxes assessed by your local government. These are often collected by the lender in an escrow account and paid on your behalf annually or semi-annually.
Insurance: Homeowners insurance protects your property against damage. Like taxes, this is usually bundled into your monthly payment via escrow.
How Interest Rates Affect Your Buying Power
Even a small change in interest rates can significantly impact your monthly payment and the total cost of the loan. For example, on a $300,000 loan, a 1% increase in interest rate can increase your monthly payment by approximately $150 to $200, depending on the term. It is crucial to shop around for the best rate and improve your credit score before applying.
What is Private Mortgage Insurance (PMI)?
If your down payment is less than 20% of the home's purchase price, lenders typically require Private Mortgage Insurance (PMI). This protects the lender if you default on the loan. While this calculator focuses on PITI and HOA, remember to factor in PMI costs if you are making a low down payment (typically 0.5% to 1% of the loan amount annually).
Using This Calculator
To get the most accurate result, enter your expected home price and down payment. Don't forget to include accurate estimates for property taxes and home insurance, as these vary widely by location. If you are buying a condo or a home in a planned community, be sure to add the monthly HOA (Homeowners Association) fees, as these are paid in addition to your mortgage but affect your debt-to-income ratio.
function calculateMortgage() {
// 1. Get Input Values
var homePrice = parseFloat(document.getElementById('homePrice').value);
var downPayment = parseFloat(document.getElementById('downPayment').value);
var annualRate = parseFloat(document.getElementById('interestRate').value);
var years = parseFloat(document.getElementById('loanTerm').value);
var annualTax = parseFloat(document.getElementById('propertyTax').value);
var annualInsurance = parseFloat(document.getElementById('homeInsurance').value);
var monthlyHOA = parseFloat(document.getElementById('hoaFees').value);
// 2. Input Validation
if (isNaN(homePrice) || homePrice <= 0) {
alert("Please enter a valid Home Price.");
return;
}
if (isNaN(downPayment) || downPayment < 0) {
downPayment = 0;
}
if (isNaN(annualRate) || annualRate < 0) {
alert("Please enter a valid Interest Rate.");
return;
}
if (isNaN(years) || years <= 0) {
alert("Please enter a valid Loan Term.");
return;
}
// Handle optional fields defaults
if (isNaN(annualTax)) annualTax = 0;
if (isNaN(annualInsurance)) annualInsurance = 0;
if (isNaN(monthlyHOA)) monthlyHOA = 0;
// 3. Core Calculations
var loanAmount = homePrice – downPayment;
// If down payment is greater than home price
if (loanAmount < 0) {
alert("Down payment cannot be greater than the Home Price.");
return;
}
var monthlyRate = (annualRate / 100) / 12;
var numberOfPayments = years * 12;
var monthlyPrincipalInterest = 0;
// Mortgage Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
if (annualRate === 0) {
monthlyPrincipalInterest = loanAmount / numberOfPayments;
} else {
monthlyPrincipalInterest = loanAmount *
(monthlyRate * Math.pow(1 + monthlyRate, numberOfPayments)) /
(Math.pow(1 + monthlyRate, numberOfPayments) – 1);
}
// Monthly Tax and Insurance
var monthlyTax = annualTax / 12;
var monthlyInsurance = annualInsurance / 12;
var totalMonthlyPayment = monthlyPrincipalInterest + monthlyTax + monthlyInsurance + monthlyHOA;
// Total Loan Cost Calculations
var totalPrincipalInterestPaid = monthlyPrincipalInterest * numberOfPayments;
var totalInterestPaid = totalPrincipalInterestPaid – loanAmount;
var totalCostOfLoan = totalPrincipalInterestPaid + (monthlyTax * numberOfPayments) + (monthlyInsurance * numberOfPayments) + (monthlyHOA * numberOfPayments);
// 4. Update UI
document.getElementById('resPrincipalInterest').innerText = "$" + monthlyPrincipalInterest.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resPropertyTax').innerText = "$" + monthlyTax.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resHomeInsurance').innerText = "$" + monthlyInsurance.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resHOA').innerText = "$" + monthlyHOA.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resTotal').innerText = "$" + totalMonthlyPayment.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
// Summary Section
document.getElementById('resLoanAmount').innerText = "$" + loanAmount.toLocaleString('en-US', {minimumFractionDigits: 0, maximumFractionDigits: 0});
document.getElementById('resTotalInterest').innerText = "$" + totalInterestPaid.toLocaleString('en-US', {minimumFractionDigits: 0, maximumFractionDigits: 0});
document.getElementById('resTotalCost').innerText = "$" + totalPrincipalInterestPaid.toLocaleString('en-US', {minimumFractionDigits: 0, maximumFractionDigits: 0}) + " (Principal + Interest)";
// Show results area
document.getElementById('results-area').style.display = 'block';
}