Estimate your monthly mortgage payments including tax and insurance.
30 Years
20 Years
15 Years
10 Years
Please enter valid positive numbers for all fields.
Estimated Monthly Payment$0.00
Principal & Interest$0.00
Property Tax (Monthly)$0.00
Home Insurance (Monthly)$0.00
Loan Amount$0.00
Total Interest Paid$0.00
Understanding Your Mortgage Calculation
Using a reliable Mortgage Calculator is the first step in the home buying journey. This tool helps you understand exactly how much house you can afford by breaking down the monthly costs associated with a home loan.
How is the Monthly Payment Calculated?
Your monthly mortgage payment is primarily composed of four parts, often referred to as PITI:
Principal: The portion of your payment that goes toward paying down the original amount borrowed.
Interest: The cost of borrowing money from your lender, calculated as a percentage of the remaining principal.
Taxes: Property taxes assessed by your local government, typically collected by the lender in escrow and paid annually.
Insurance: Homeowners insurance to protect your property against damage, also usually paid through escrow.
The Impact of Interest Rates
Even a small difference in the Interest Rate can have a massive impact on your monthly payment and the total cost of the loan over time. For example, on a $300,000 loan, a difference of just 1% in the interest rate can change your monthly payment by hundreds of dollars and your total interest paid by tens of thousands.
Loan Term: 15 vs. 30 Years
Choosing between a 15-year and a 30-year term is a common dilemma. A 30-year mortgage offers lower monthly payments, making the home more affordable on a monthly basis, but you will pay significantly more in interest over the life of the loan. Conversely, a 15-year mortgage has higher monthly payments but allows you to build equity faster and save money on interest.
Why Include Taxes and Insurance?
Many simple calculators only show Principal and Interest. However, most lenders require an escrow account for taxes and insurance, meaning these costs are part of the check you write every month. Excluding them can lead to "payment shock" when you actually sign your closing papers. Our calculator includes these variables to give you a realistic view of your housing budget.
function calculateMortgage() {
// 1. 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 termYears = parseInt(document.getElementById("loanTerm").value);
var annualTax = parseFloat(document.getElementById("propertyTax").value);
var annualInsurance = parseFloat(document.getElementById("insurance").value);
// 2. DOM Elements for Results
var resultBox = document.getElementById("resultBox");
var errorMsg = document.getElementById("errorMsg");
var monthlyTotalEl = document.getElementById("monthlyTotal");
var piAmountEl = document.getElementById("piAmount");
var taxAmountEl = document.getElementById("taxAmount");
var insAmountEl = document.getElementById("insAmount");
var loanAmountEl = document.getElementById("loanAmountResult");
var totalInterestEl = document.getElementById("totalInterestResult");
// 3. Validation
if (isNaN(homePrice) || isNaN(downPayment) || isNaN(interestRate) || isNaN(termYears) ||
homePrice < 0 || downPayment < 0 || interestRate = homePrice) {
errorMsg.innerText = "Down payment cannot be greater than or equal to home price.";
errorMsg.style.display = "block";
resultBox.style.display = "none";
return;
} else {
errorMsg.innerText = "Please enter valid positive numbers for all fields."; // Reset error text
errorMsg.style.display = "none";
}
// 4. Calculations
var principal = homePrice – downPayment;
var monthlyRate = (interestRate / 100) / 12;
var numberOfPayments = termYears * 12;
var monthlyPI = 0;
// Handle 0% interest edge case
if (interestRate === 0) {
monthlyPI = principal / numberOfPayments;
} else {
// Standard Mortgage Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
var mathPower = Math.pow(1 + monthlyRate, numberOfPayments);
monthlyPI = principal * ((monthlyRate * mathPower) / (mathPower – 1));
}
var monthlyTax = 0;
if (!isNaN(annualTax)) {
monthlyTax = annualTax / 12;
}
var monthlyInsurance = 0;
if (!isNaN(annualInsurance)) {
monthlyInsurance = annualInsurance / 12;
}
var totalMonthlyPayment = monthlyPI + monthlyTax + monthlyInsurance;
var totalCostOfLoan = (monthlyPI * numberOfPayments);
var totalInterest = totalCostOfLoan – principal;
// 5. Formatting Output
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 2
});
// 6. Display Results
monthlyTotalEl.innerText = formatter.format(totalMonthlyPayment);
piAmountEl.innerText = formatter.format(monthlyPI);
taxAmountEl.innerText = formatter.format(monthlyTax);
insAmountEl.innerText = formatter.format(monthlyInsurance);
loanAmountEl.innerText = formatter.format(principal);
totalInterestEl.innerText = formatter.format(totalInterest);
resultBox.style.display = "block";
}