Estimate your monthly mortgage payments including principal, interest, taxes, and insurance (PITI).
Monthly Payment: $0.00
Principal & Interest:$0.00
Property Tax:$0.00
Home Insurance:$0.00
Total Interest Paid (Over Term):$0.00
Total Cost of Loan:$0.00
Understanding Your Mortgage Calculation
Buying a home is one of the largest financial decisions most people make. Understanding the components of your monthly mortgage payment is crucial for budgeting and financial planning. This calculator breaks down the "PITI" (Principal, Interest, Taxes, and Insurance) to give you a realistic view of your housing costs.
Expert Tip: Don't just look at the Principal and Interest. Taxes and insurance can add 20-30% to your monthly bill, significantly affecting home affordability.
The 4 Pillars of a Mortgage Payment (PITI)
Principal: The portion of your payment that goes toward paying down the original amount you borrowed. In the early years of a loan, this amount is small but grows over time.
Interest: The cost of borrowing money. This is calculated based on your remaining loan balance and your annual interest rate.
Taxes: Property taxes assessed by your local government. These are typically collected by your lender in an escrow account and paid annually on your behalf.
Insurance: Homeowners insurance protects your property against damage. Like taxes, this is usually part of your monthly escrow payment.
How Interest Rates Affect Affordability
Even a small change in interest rates can have a massive impact on your monthly payment and the total cost of the loan. For example, on a $300,000 loan, the difference between a 6% and a 7% interest rate is roughly $200 per month and over $70,000 in total interest paid over 30 years.
What is an Amortization Schedule?
Amortization refers to the process of paying off a debt over time through regular payments. A 30-year fixed-rate mortgage is fully amortized, meaning that if you make every scheduled payment, the balance will be exactly zero at the end of the term. Initially, your payments are mostly interest, but as the principal balance decreases, the interest portion shrinks, and more of your payment goes toward equity.
function calculateMortgage() {
// Get Input Values
var homePrice = parseFloat(document.getElementById('homePrice').value);
var downPayment = parseFloat(document.getElementById('downPayment').value);
var interestRate = parseFloat(document.getElementById('interestRate').value);
var loanTerm = parseFloat(document.getElementById('loanTerm').value);
var propertyTaxAnnual = parseFloat(document.getElementById('propertyTax').value);
var homeInsuranceAnnual = parseFloat(document.getElementById('homeInsurance').value);
// Validation
if (isNaN(homePrice) || isNaN(downPayment) || isNaN(interestRate) || isNaN(loanTerm)) {
alert("Please enter valid numbers for all fields.");
return;
}
if (downPayment >= homePrice) {
alert("Down payment cannot be greater than or equal to the home price.");
return;
}
// Core Calculations
var principal = homePrice – downPayment;
var monthlyRate = (interestRate / 100) / 12;
var numberOfPayments = loanTerm * 12;
// Monthly P&I Calculation
// Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
var monthlyPI = 0;
if (interestRate === 0) {
monthlyPI = principal / numberOfPayments;
} else {
monthlyPI = principal * (monthlyRate * Math.pow(1 + monthlyRate, numberOfPayments)) / (Math.pow(1 + monthlyRate, numberOfPayments) – 1);
}
// Escrow Calculations (Tax & Insurance)
var monthlyTax = propertyTaxAnnual / 12;
var monthlyInsurance = homeInsuranceAnnual / 12;
// Total Monthly Payment
var totalMonthlyPayment = monthlyPI + monthlyTax + monthlyInsurance;
// Total Cost Calculations
var totalPrincipalAndInterest = monthlyPI * numberOfPayments;
var totalInterestPaid = totalPrincipalAndInterest – principal;
var totalCostOfLoan = totalPrincipalAndInterest + (monthlyTax * numberOfPayments) + (monthlyInsurance * numberOfPayments);
// Update UI
document.getElementById('monthlyTotal').innerText = formatCurrency(totalMonthlyPayment);
document.getElementById('monthlyPI').innerText = formatCurrency(monthlyPI);
document.getElementById('monthlyTax').innerText = formatCurrency(monthlyTax);
document.getElementById('monthlyIns').innerText = formatCurrency(monthlyInsurance);
document.getElementById('totalInterest').innerText = formatCurrency(totalInterestPaid);
document.getElementById('totalCost').innerText = formatCurrency(totalCostOfLoan);
// Show Results Area
document.getElementById('results-area').style.display = "block";
}
function formatCurrency(num) {
return new Intl.NumberFormat('en-US', { style: 'currency', currency: 'USD' }).format(num);
}