Purchasing a home is one of the most significant financial decisions you will make. This Mortgage Payment Calculator helps you estimate your monthly housing costs by factoring in the home price, down payment, interest rate, loan term, and additional expenses like property taxes and homeowners insurance.
How is the Monthly Payment Calculated?
The core of a mortgage payment typically consists of four parts, often referred to as PITI:
Principal: The portion of your payment that reduces the loan balance.
Interest: The cost of borrowing money from your lender.
Taxes: Property taxes assessed by your local government, usually held in escrow.
Insurance: Homeowners insurance to protect the property against damage.
Why Your Interest Rate Matters
Even a small difference in your interest rate can have a massive impact on your total loan cost over 15 or 30 years. For example, on a $300,000 loan, a 1% difference in rate can change your monthly payment by hundreds of dollars and your total interest paid by tens of thousands.
Calculating Amortization
Most fixed-rate mortgages use an amortization formula. In the early years of your loan, the majority of your payment goes toward interest. As time passes, a larger portion applies to the principal. Use this calculator to see exactly how much total interest you will pay over the life of the loan.
Tips for Lowering Your Payment
If the estimated payment is higher than your budget allows, consider increasing your down payment to lower the principal amount, shopping for a lower interest rate, or extending the loan term (though this will increase the total interest paid in the long run).
function calculateMortgage() {
// 1. Get Input Values
var price = parseFloat(document.getElementById('homePrice').value);
var down = parseFloat(document.getElementById('downPayment').value);
var rate = parseFloat(document.getElementById('interestRate').value);
var years = parseFloat(document.getElementById('loanTerm').value);
var tax = parseFloat(document.getElementById('propertyTax').value);
var insurance = parseFloat(document.getElementById('homeInsurance').value);
var errorDiv = document.getElementById('errorMsg');
var resultsDiv = document.getElementById('resultsSection');
// 2. Validation
if (isNaN(price) || isNaN(down) || isNaN(rate) || isNaN(years) || price <= 0 || years = price) {
errorDiv.innerHTML = "Down payment cannot be greater than or equal to home price.";
errorDiv.style.display = 'block';
resultsDiv.style.display = 'none';
return;
} else {
errorDiv.style.display = 'none';
}
// 3. Calculation Logic
var principal = price – down;
var monthlyRate = (rate / 100) / 12;
var numberOfPayments = years * 12;
var monthlyPI = 0;
// Handle zero interest case
if (rate === 0) {
monthlyPI = principal / numberOfPayments;
} else {
// Standard Mortgage Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
monthlyPI = principal * ( (monthlyRate * Math.pow(1 + monthlyRate, numberOfPayments)) / (Math.pow(1 + monthlyRate, numberOfPayments) – 1) );
}
// Calculate Monthly Tax and Insurance
var monthlyTax = (isNaN(tax) ? 0 : tax) / 12;
var monthlyInsurance = (isNaN(insurance) ? 0 : insurance) / 12;
var totalMonthly = monthlyPI + monthlyTax + monthlyInsurance;
var totalCost = monthlyPI * numberOfPayments;
var totalInterest = totalCost – principal;
// Calculate Payoff Date
var today = new Date();
var payoffDate = new Date(today.setMonth(today.getMonth() + numberOfPayments));
var options = { month: 'long', year: 'numeric' };
var payoffString = payoffDate.toLocaleDateString('en-US', options);
// 4. Update UI
document.getElementById('totalMonthlyDisplay').innerText = formatCurrency(totalMonthly);
document.getElementById('principalInterestDisplay').innerText = formatCurrency(monthlyPI);
document.getElementById('taxInsuranceDisplay').innerText = formatCurrency(monthlyTax + monthlyInsurance);
document.getElementById('totalInterestDisplay').innerText = formatCurrency(totalInterest);
document.getElementById('payoffDateDisplay').innerText = payoffString;
// Show results
resultsDiv.style.display = 'block';
}
function formatCurrency(num) {
return '$' + num.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
}
// Initialize logic on load for the default values (optional, or just wait for click)
// Here we wait for click as per standard calculator behavior