Please enter valid positive numbers for all fields.
Payment Breakdown
Principal & Interest:$0.00
Monthly Property Tax:$0.00
Monthly Home Insurance:$0.00
Loan Amount:$0.00
Estimated Monthly Payment
$0.00
Understanding Your Mortgage Calculation
Buying a home is often the largest financial decision a person will make. Using a comprehensive Mortgage Payment Calculator is essential to understand exactly how much you will be paying each month, beyond just the listing price of the house.
The Components of a Mortgage Payment (PITI)
Most mortgage payments are made up of four key components, commonly referred to as PITI:
Principal: The portion of your payment that reduces the loan balance.
Interest: The cost of borrowing money, paid to the lender.
Taxes: Property taxes charged by your local government, usually collected by the lender in an escrow account.
Insurance: Homeowners insurance to protect the property against damage.
How the Mortgage Formula Works
The standard formula used to calculate the monthly principal and interest payment is:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
Where:
M is the total monthly mortgage payment.
P is the principal loan amount (Home Price minus Down Payment).
i is the monthly interest rate (Annual Rate divided by 12 months).
n is the number of payments (Loan Term in years multiplied by 12).
Impact of Interest Rates and Loan Terms
Even a small difference in your interest rate can significantly impact your monthly payment and the total interest paid over the life of the loan. For example, on a $300,000 loan, the difference between a 6.0% and a 7.0% interest rate can equate to hundreds of dollars per month. Similarly, choosing a 15-year term instead of a 30-year term will increase your monthly obligation but drastically reduce the total interest paid.
Additional Costs to Consider
While this calculator covers the core PITI, remember to budget for other expenses such as HOA fees, private mortgage insurance (PMI) if your down payment is less than 20%, and ongoing maintenance costs. Understanding these figures helps ensure that your dream home remains a financial asset rather than a liability.
function calculateMortgage() {
// Get input elements by ID
var priceInput = document.getElementById("mc_home_price");
var downInput = document.getElementById("mc_down_payment");
var rateInput = document.getElementById("mc_interest_rate");
var termInput = document.getElementById("mc_loan_term");
var taxInput = document.getElementById("mc_property_tax");
var insuranceInput = document.getElementById("mc_insurance");
// Parse values
var homePrice = parseFloat(priceInput.value);
var downPayment = parseFloat(downInput.value);
var interestRate = parseFloat(rateInput.value);
var years = parseFloat(termInput.value);
var annualTax = parseFloat(taxInput.value);
var annualInsurance = parseFloat(insuranceInput.value);
// Validation
var errorDiv = document.getElementById("mc_error_msg");
var resultDiv = document.getElementById("mc_result_area");
if (isNaN(homePrice) || isNaN(downPayment) || isNaN(interestRate) || isNaN(years) ||
isNaN(annualTax) || isNaN(annualInsurance) || homePrice <= 0 || years = homePrice) {
errorDiv.innerHTML = "Down payment cannot be greater than or equal to Home Price.";
errorDiv.style.display = "block";
resultDiv.style.display = "none";
return;
} else {
errorDiv.innerHTML = "Please enter valid positive numbers for all fields.";
errorDiv.style.display = "none";
}
// Calculations
var principal = homePrice – downPayment;
var monthlyRate = (interestRate / 100) / 12;
var numberOfPayments = years * 12;
var monthlyTax = annualTax / 12;
var monthlyInsurance = annualInsurance / 12;
var monthlyPrincipalInterest = 0;
// Prevent division by zero if rate is 0
if (interestRate === 0) {
monthlyPrincipalInterest = principal / numberOfPayments;
} else {
// Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
var x = Math.pow(1 + monthlyRate, numberOfPayments);
monthlyPrincipalInterest = (principal * x * monthlyRate) / (x – 1);
}
var totalMonthlyPayment = monthlyPrincipalInterest + monthlyTax + monthlyInsurance;
// Display Results
document.getElementById("mc_val_loan_amount").innerText = "$" + principal.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("mc_val_principal_interest").innerText = "$" + monthlyPrincipalInterest.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("mc_val_tax").innerText = "$" + monthlyTax.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("mc_val_insurance").innerText = "$" + monthlyInsurance.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("mc_val_total").innerText = "$" + totalMonthlyPayment.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
resultDiv.style.display = "block";
}