Please enter valid positive numbers for all fields.
Monthly Principal & Interest:$0.00
Monthly Tax & Insurance:$0.00
Monthly HOA:$0.00
Total Monthly Payment:$0.00
Total Interest Paid (Over Loan Term):$0.00
Understanding Your Mortgage Calculation
Buying a home is one of the most significant financial decisions you will make. This Mortgage Payment Calculator helps you estimate your monthly financial commitment by breaking down the key components of a mortgage loan: Principal, Interest, Taxes, and Insurance (often referred to as PITI).
How the Formula Works
While the calculation of a mortgage payment might seem complex, it follows a standard amortization formula. The core calculation determines the monthly principal and interest payment required to pay off the loan balance over the selected term (usually 15 or 30 years) at a fixed interest rate.
The basic components are:
Principal: The amount of money you borrow (Home Price minus Down Payment).
Interest: The cost of borrowing money, expressed as a percentage rate.
Taxes: Property taxes charged by your local municipality, usually assessed annually but paid monthly into an escrow account.
Insurance: Homeowners insurance to protect the property, also typically paid monthly via escrow.
Why Your Monthly Payment Varies
Many homebuyers focus solely on the interest rate, but other factors significantly impact your monthly cash flow:
Loan Term: A 30-year term offers lower monthly payments but results in significantly more interest paid over the life of the loan compared to a 15-year term.
Down Payment: A larger down payment reduces the principal loan amount, lowering both your monthly payment and the total interest costs. Additionally, putting down less than 20% often triggers Private Mortgage Insurance (PMI), which is an extra cost not included in the standard calculation above.
Property Taxes & HOA: In high-tax areas or communities with expensive Homeowners Association (HOA) fees, these non-mortgage costs can sometimes equal or exceed the principal repayment portion of your bill.
Tips for Lowering Your Mortgage Costs
To secure a more affordable mortgage, consider improving your credit score to qualify for lower interest rates. Even a fraction of a percentage point reduction can save tens of thousands of dollars over 30 years. Additionally, shopping around for cheaper homeowners insurance and appealing property tax assessments can help manage the escrow portion of your monthly payment.
function calculateMortgage() {
// 1. Get Input Values
var homePrice = parseFloat(document.getElementById('mc_home_price').value);
var downPayment = parseFloat(document.getElementById('mc_down_payment').value);
var interestRate = parseFloat(document.getElementById('mc_interest_rate').value);
var loanTermYears = parseInt(document.getElementById('mc_loan_term').value);
var annualTax = parseFloat(document.getElementById('mc_property_tax').value);
var annualInsurance = parseFloat(document.getElementById('mc_insurance').value);
var monthlyHOA = parseFloat(document.getElementById('mc_hoa').value);
var errorDiv = document.getElementById('mc_error');
var resultsDiv = document.getElementById('mc_results');
// 2. Validation
if (isNaN(homePrice) || isNaN(downPayment) || isNaN(interestRate) ||
isNaN(loanTermYears) || isNaN(annualTax) || isNaN(annualInsurance) || isNaN(monthlyHOA)) {
errorDiv.style.display = 'block';
resultsDiv.style.display = 'none';
return;
}
if (homePrice < 0 || downPayment < 0 || interestRate < 0) {
errorDiv.style.display = 'block';
resultsDiv.style.display = 'none';
return;
}
errorDiv.style.display = 'none';
// 3. Calculation Logic
var principal = homePrice – downPayment;
// Handle case where down payment exceeds home price
if (principal < 0) principal = 0;
var monthlyInterestRate = (interestRate / 100) / 12;
var numberOfPayments = loanTermYears * 12;
var monthlyPrincipalInterest = 0;
// Special case for 0% interest
if (interestRate === 0) {
monthlyPrincipalInterest = principal / numberOfPayments;
} else {
// Standard Mortgage Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
var x = Math.pow(1 + monthlyInterestRate, numberOfPayments);
monthlyPrincipalInterest = (principal * x * monthlyInterestRate) / (x – 1);
}
var monthlyTax = annualTax / 12;
var monthlyInsurance = annualInsurance / 12;
var totalMonthlyPayment = monthlyPrincipalInterest + monthlyTax + monthlyInsurance + monthlyHOA;
var totalAmountPaid = (monthlyPrincipalInterest * numberOfPayments);
var totalInterestPaid = totalAmountPaid – principal;
// 4. Update UI
// Format as Currency USD
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 2
});
document.getElementById('res_principal_interest').innerText = formatter.format(monthlyPrincipalInterest);
document.getElementById('res_tax_ins').innerText = formatter.format(monthlyTax + monthlyInsurance);
document.getElementById('res_hoa').innerText = formatter.format(monthlyHOA);
document.getElementById('res_total_monthly').innerText = formatter.format(totalMonthlyPayment);
document.getElementById('res_total_interest').innerText = formatter.format(totalInterestPaid);
resultsDiv.style.display = 'block';
}