Estimate your monthly home loan payments including principal, interest, taxes, and insurance.
Principal & Interest:$0.00
Monthly Tax:$0.00
Monthly Insurance:$0.00
Total Monthly Payment:$0.00
How to Calculate Your Mortgage Payment
Understanding your monthly mortgage obligation is the most critical step in the home-buying process. This calculator uses the standard amortization formula to determine your monthly Principal and Interest (P&I), while also factoring in escrow items like property taxes and homeowners insurance.
The Mortgage Formula Explained
The core of your payment is calculated using the following formula:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
M: Total monthly payment.
P: Principal loan amount (Home price minus down payment).
i: Monthly interest rate (Annual rate divided by 12).
n: Number of months in the loan term (Years multiplied by 12).
Example Calculation
If you purchase a home for $400,000 with a $80,000 down payment (20%), your loan amount (Principal) is $320,000. At a 6.5% interest rate for 30 years:
Beyond the home price, several factors significantly impact your final monthly check:
Down Payment: A larger down payment reduces your loan principal and may eliminate the need for Private Mortgage Insurance (PMI).
Interest Rate: Even a 0.5% difference in your interest rate can save or cost you tens of thousands of dollars over the life of the loan.
Loan Term: A 15-year mortgage will have higher monthly payments but significantly lower total interest paid compared to a 30-year mortgage.
Escrow: Most lenders require you to pay property taxes and insurance into an escrow account monthly, which they then pay to the government and insurance company on your behalf.
function calculateMortgage() {
var homePrice = parseFloat(document.getElementById('homePrice').value);
var downPayment = parseFloat(document.getElementById('downPayment').value);
var loanTerm = parseFloat(document.getElementById('loanTerm').value);
var annualRate = parseFloat(document.getElementById('interestRate').value);
var propertyTax = parseFloat(document.getElementById('propertyTax').value);
var insurance = parseFloat(document.getElementById('insurance').value);
if (isNaN(homePrice) || isNaN(downPayment) || isNaN(loanTerm) || isNaN(annualRate)) {
alert("Please enter valid numbers in all required fields.");
return;
}
var principal = homePrice – downPayment;
if (principal <= 0) {
alert("Down payment cannot be greater than or equal to the home price.");
return;
}
var monthlyRate = (annualRate / 100) / 12;
var numberOfPayments = loanTerm * 12;
// Monthly P&I Calculation
var x = Math.pow(1 + monthlyRate, numberOfPayments);
var monthlyPI = (principal * x * monthlyRate) / (x – 1);
// Monthly Escrow
var monthlyTax = propertyTax / 12;
var monthlyIns = insurance / 12;
var totalMonthly = monthlyPI + monthlyTax + monthlyIns;
// Formatting
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
});
document.getElementById('resPI').innerText = formatter.format(monthlyPI);
document.getElementById('resTax').innerText = formatter.format(monthlyTax);
document.getElementById('resIns').innerText = formatter.format(monthlyIns);
document.getElementById('resTotal').innerText = formatter.format(totalMonthly);
document.getElementById('result-box').style.display = 'block';
}