Buying a home is one of the most significant financial decisions you will make. This Mortgage Calculator is designed to help you estimate your monthly payments and understand the long-term cost of borrowing money for a property. By inputting your home price, down payment, interest rate, and term, you can instantly see how these variables affect your budget.
How Is Your Monthly Payment Calculated?
A standard mortgage payment typically consists of four main components, often referred to as PITI:
Principal: The money that goes towards paying down the balance of the loan.
Interest: The cost of borrowing the money, paid to the lender.
Taxes: Property taxes assessed by your local government, often held in escrow by the lender.
Insurance: Homeowners insurance to protect the property against hazards.
This calculator uses the standard amortization formula to determine the Principal and Interest (P&I) portion, and then adds the monthly pro-rated amounts for property tax and home insurance to give you a complete picture of your monthly obligation.
Example Calculation
Consider a scenario where you purchase a home for $350,000 with a $70,000 down payment (20%). This leaves a loan amount of $280,000. If you secure a 30-year fixed-rate mortgage at an interest rate of 6.5%:
Your monthly Principal & Interest payment would be approximately $1,770.
Over the life of the loan, you would pay approximately $357,000 in interest alone.
Adding annual property taxes (e.g., $3,500) and insurance (e.g., $1,200) would increase your monthly outlay by about $392, bringing the total estimated monthly payment to $2,162.
Why Interest Rates Matter
Even a small difference in interest rates can have a massive impact on the total cost of your home. For example, on a $300,000 loan, the difference between a 6% and a 7% interest rate can amount to over $60,000 in additional interest paid over 30 years. Using this calculator allows you to compare different rate scenarios to see how much house you can truly afford.
function calculateMortgage() {
// 1. Get input values by ID
var homePriceInput = document.getElementById("homePrice");
var downPaymentInput = document.getElementById("downPayment");
var loanTermInput = document.getElementById("loanTerm");
var interestRateInput = document.getElementById("interestRate");
var propertyTaxInput = document.getElementById("propertyTax");
var homeInsuranceInput = document.getElementById("homeInsurance");
// 2. Parse values (handle empty inputs with defaults or 0)
var homePrice = parseFloat(homePriceInput.value);
var downPayment = parseFloat(downPaymentInput.value);
var years = parseFloat(loanTermInput.value);
var annualRate = parseFloat(interestRateInput.value);
var annualTax = parseFloat(propertyTaxInput.value);
var annualInsurance = parseFloat(homeInsuranceInput.value);
// Validate core numbers
if (isNaN(homePrice) || isNaN(downPayment) || isNaN(years) || isNaN(annualRate)) {
alert("Please enter valid numbers for Home Price, Down Payment, Term, and Interest Rate.");
return;
}
// Handle optional fields
if (isNaN(annualTax)) annualTax = 0;
if (isNaN(annualInsurance)) annualInsurance = 0;
// 3. Calculation Logic
var loanAmount = homePrice – downPayment;
// Prevent negative loan amounts
if (loanAmount <= 0) {
alert("Down payment cannot be greater than or equal to the Home Price.");
return;
}
var monthlyRate = (annualRate / 100) / 12;
var numberOfPayments = years * 12;
var monthlyPI = 0;
// Handle 0% interest edge case
if (annualRate === 0) {
monthlyPI = loanAmount / numberOfPayments;
} else {
// Mortgage Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
var numerator = monthlyRate * Math.pow((1 + monthlyRate), numberOfPayments);
var denominator = Math.pow((1 + monthlyRate), numberOfPayments) – 1;
monthlyPI = loanAmount * (numerator / denominator);
}
var monthlyTax = annualTax / 12;
var monthlyInsurance = annualInsurance / 12;
var totalMonthlyPayment = monthlyPI + monthlyTax + monthlyInsurance;
var totalPaymentOverLife = (monthlyPI * numberOfPayments);
var totalInterest = totalPaymentOverLife – loanAmount;
var totalCost = totalPaymentOverLife + downPayment + (annualTax * years) + (annualInsurance * years);
// 4. Update UI
// Helper for currency formatting
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 2
});
document.getElementById("monthlyPaymentDisplay").innerHTML = formatter.format(totalMonthlyPayment);
document.getElementById("piDisplay").innerHTML = formatter.format(monthlyPI);
document.getElementById("loanAmountDisplay").innerHTML = formatter.format(loanAmount);
document.getElementById("totalInterestDisplay").innerHTML = formatter.format(totalInterest);
document.getElementById("totalCostDisplay").innerHTML = formatter.format(totalCost);
// Show results
document.getElementById("resultContainer").style.display = "block";
}
{
"@context": "https://schema.org",
"@type": "FAQPage",
"mainEntity": [{
"@type": "Question",
"name": "How is a mortgage payment calculated?",
"acceptedAnswer": {
"@type": "Answer",
"text": "A mortgage payment is calculated using the principal loan amount, the interest rate, and the loan term. The formula amortizes the loan so equal payments are made monthly, consisting of interest and principal repayment. Property taxes and insurance are often added."
}
}, {
"@type": "Question",
"name": "Does down payment affect monthly mortgage payments?",
"acceptedAnswer": {
"@type": "Answer",
"text": "Yes. A larger down payment reduces the principal loan amount, which lowers the monthly interest and principal payment. It may also remove the need for Private Mortgage Insurance (PMI)."
}
}, {
"@type": "Question",
"name": "What is included in PITI?",
"acceptedAnswer": {
"@type": "Answer",
"text": "PITI stands for Principal, Interest, Taxes, and Insurance. These are the four primary components that make up a standard monthly mortgage payment."
}
}]
}