Estimate your monthly payments including principal, interest, taxes, and insurance.
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Loan Amount:$0.00
Principal & Interest:$0.00
Property Tax (Monthly):$0.00
Home Insurance (Monthly):$0.00
HOA Fees:$0.00
Total Monthly Payment:$0.00
Total Interest Paid: $0.00
Understanding Your Mortgage Calculation
Calculating your monthly mortgage payment involves more than just repaying the bank for the money you borrowed. A complete picture of your monthly housing costs, often referred to as PITI (Principal, Interest, Taxes, and Insurance), is essential for accurate budgeting.
How the Formula Works
This calculator uses the standard amortization formula to determine your base monthly payment:
Principal: The money deducted from the original loan balance.
Interest: The fee charged by the lender for borrowing the money.
Additionally, we factor in escrow items like property taxes and homeowners insurance, which are typically collected by your lender in monthly installments, as well as Homeowners Association (HOA) fees which are paid separately.
Factors Affecting Your Payment
Down Payment: putting more money down reduces your loan amount, which lowers your monthly principal and interest payment. It may also eliminate the need for Private Mortgage Insurance (PMI).
Interest Rate: 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.
Loan Term: A 30-year term offers lower monthly payments but results in higher total interest costs compared to a 15-year term.
What is PITI?
PITI stands for Principal, Interest, Taxes, and Insurance. Lenders look at PITI when deciding whether you qualify for a mortgage. Ideally, your PITI should not exceed 28% of your gross monthly income.
Definitions
Property Tax: Taxes paid to your local government based on the assessed value of your home. This calculator divides your yearly tax bill by 12.
Homeowners Insurance: Protects your home against damages. Like taxes, this is often paid annually but collected monthly.
HOA Fees: If you buy a condo or a home in a planned community, you may have to pay monthly fees for common area maintenance.
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 loanTermYears = parseFloat(document.getElementById("loanTerm").value);
var propertyTaxYearly = parseFloat(document.getElementById("propertyTax").value);
var homeInsuranceYearly = parseFloat(document.getElementById("homeInsurance").value);
var hoaFeesMonthly = parseFloat(document.getElementById("hoaFees").value);
// 2. Validate Inputs
if (isNaN(homePrice) || homePrice <= 0) homePrice = 0;
if (isNaN(downPayment) || downPayment < 0) downPayment = 0;
if (isNaN(interestRate) || interestRate < 0) interestRate = 0;
if (isNaN(loanTermYears) || loanTermYears <= 0) loanTermYears = 30;
if (isNaN(propertyTaxYearly) || propertyTaxYearly < 0) propertyTaxYearly = 0;
if (isNaN(homeInsuranceYearly) || homeInsuranceYearly < 0) homeInsuranceYearly = 0;
if (isNaN(hoaFeesMonthly) || hoaFeesMonthly < 0) hoaFeesMonthly = 0;
// 3. Perform Calculations
var loanAmount = homePrice – downPayment;
// Prevent negative loan amount
if (loanAmount < 0) loanAmount = 0;
// Monthly Interest Rate (r) and Total Number of Payments (n)
var monthlyRate = (interestRate / 100) / 12;
var numberOfPayments = loanTermYears * 12;
// Calculate Monthly Principal & Interest (Amortization Formula)
// M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
var monthlyPrincipalInterest = 0;
if (interestRate === 0) {
monthlyPrincipalInterest = loanAmount / numberOfPayments;
} else {
var mathPower = Math.pow(1 + monthlyRate, numberOfPayments);
monthlyPrincipalInterest = loanAmount * ((monthlyRate * mathPower) / (mathPower – 1));
}
if (isNaN(monthlyPrincipalInterest)) monthlyPrincipalInterest = 0;
// Calculate Monthly Tax and Insurance
var monthlyTax = propertyTaxYearly / 12;
var monthlyInsurance = homeInsuranceYearly / 12;
// Calculate Total Monthly Payment
var totalMonthlyPayment = monthlyPrincipalInterest + monthlyTax + monthlyInsurance + hoaFeesMonthly;
// Calculate Total Interest Paid
var totalRepayment = monthlyPrincipalInterest * numberOfPayments;
var totalInterest = totalRepayment – loanAmount;
if (totalInterest < 0) totalInterest = 0;
// 4. Update UI
// Format Currency Function
function formatMoney(amount) {
return "$" + amount.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
}
document.getElementById("resLoanAmount").innerHTML = formatMoney(loanAmount);
document.getElementById("resPrincipalInterest").innerHTML = formatMoney(monthlyPrincipalInterest);
document.getElementById("resTax").innerHTML = formatMoney(monthlyTax);
document.getElementById("resInsurance").innerHTML = formatMoney(monthlyInsurance);
document.getElementById("resHOA").innerHTML = formatMoney(hoaFeesMonthly);
document.getElementById("resTotal").innerHTML = formatMoney(totalMonthlyPayment);
document.getElementById("resTotalInterest").innerHTML = formatMoney(totalInterest);
// Show Results Area
document.getElementById("results-area").style.display = "block";
}