Mortgage Affordability Calculator | How Much House Can I Afford?
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How Much House Can I Afford?
Use our advanced Mortgage Affordability Calculator to estimate your buying power based on the 28/36 debt-to-income rule.
Est. Monthly Mortgage Payment
$0/mo
(Includes Principal, Interest, Taxes & Insurance)
Monthly Breakdown
- Principal & Interest: $0
- Property Taxes: $0
- Homeowners Insurance: $0
- Total Housing Payment: $0
Note: Your monthly debts are high relative to your income. This significantly reduces your buying power.
Understanding Mortgage Affordability
Determining "how much house can I afford" is the first step in the home buying journey. This calculator uses industry-standard Debt-to-Income (DTI) ratios to provide a realistic estimate of your purchasing power.
The 28/36 Rule Explained
Lenders typically use two ratios to qualify you for a loan:
- Front-End Ratio (28%): The portion of your gross monthly income that goes towards housing costs (mortgage principal, interest, taxes, and insurance). Ideally, this should not exceed 28%.
- Back-End Ratio (36%): The portion of your income that goes towards all debt obligations, including housing, student loans, car payments, and credit cards. Ideally, this should not exceed 36%.
Factors That Impact Your Affordability
While your income is important, other factors play a huge role:
- Existing Debt: A high car payment or student loan reduces the amount of money available for a mortgage. Lowering your monthly debts is the fastest way to increase your home buying budget.
- Interest Rates: Even a 1% rise in interest rates can reduce your buying power by tens of thousands of dollars because more of your monthly payment goes toward interest rather than the home's principal.
- Down Payment: A larger down payment not only reduces the loan amount but may also help you avoid Private Mortgage Insurance (PMI) and secure a lower interest rate.
How to Calculate Maximum Home Price
Our calculator works backward from your monthly budget. It first calculates the maximum monthly payment lenders will allow based on your income and debts. Then, considering the interest rate, tax rate, and insurance costs, it solves for the maximum loan amount you can support. Finally, it adds your down payment to arrive at the total home price.
function calculateAffordability() {
// 1. Get Inputs
var annualIncome = parseFloat(document.getElementById("annualIncome").value);
var monthlyDebt = parseFloat(document.getElementById("monthlyDebt").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var interestRate = parseFloat(document.getElementById("interestRate").value);
var loanTermYears = parseFloat(document.getElementById("loanTerm").value);
var propertyTaxRate = parseFloat(document.getElementById("propertyTax").value);
var homeInsuranceYearly = parseFloat(document.getElementById("homeInsurance").value);
var dtiLimit = parseFloat(document.getElementById("dtiType").value);
// Validation
if (isNaN(annualIncome) || annualIncome <= 0) {
alert("Please enter a valid Annual Income.");
return;
}
// 2. Calculate Monthly Income limits
var monthlyGrossIncome = annualIncome / 12;
// Back-End Ratio Calculation (Total allowed debt payment)
var maxTotalMonthlyDebt = monthlyGrossIncome * dtiLimit;
// Front-End Ratio Calculation (Housing only limit – usually 28%)
var maxHousingFrontEnd = monthlyGrossIncome * 0.28;
// Determine maximum allowable housing payment
// We take the lesser of: (Front-End Limit) OR (Back-End Limit minus Existing Debts)
var maxHousingBackEnd = maxTotalMonthlyDebt – monthlyDebt;
// Logic: Your payment cannot exceed the front-end limit, nor can your total debt exceed back-end
// However, if the user selected "Aggressive" (FHA), front-end might be higher.
// For standard calculation, we use the constraint derived from the selected DTI limit vs debts.
var maxMonthlyPayment = maxHousingBackEnd;
// If debts are too high, max payment might be negative
if (maxMonthlyPayment <= 0) {
document.getElementById("resultPrice").innerHTML = "$0";
document.getElementById("resultPayment").innerHTML = "$0/mo";
document.getElementById("valPI").innerHTML = "$0";
document.getElementById("valTax").innerHTML = "$0";
document.getElementById("valIns").innerHTML = "$0";
document.getElementById("valTotal").innerHTML = "$0";
document.getElementById("dtiWarning").style.display = "block";
document.getElementById("dtiWarning").innerHTML = "
Critical: Your current monthly debts exceed the allowable limit for a mortgage. Consider paying down debt.";
return;
} else {
document.getElementById("dtiWarning").style.display = "none";
}
// 3. Solve for Home Price (V)
// Equation: MaxPayment = (LoanAmount * MortgageFactor) + (HomeValue * TaxRate/12) + (Insurance/12)
// LoanAmount = HomeValue – DownPayment
// var V = HomeValue, D = DownPayment, M = MortgageFactor, T = MonthlyTaxRate, I = MonthlyInsurance
// MaxPayment = ((V – D) * M) + (V * T) + I
// MaxPayment – I + (D * M) = V * (M + T)
// V = (MaxPayment – I + (D * M)) / (M + T)
var monthlyRate = (interestRate / 100) / 12;
var numPayments = loanTermYears * 12;
var monthlyTaxRate = (propertyTaxRate / 100) / 12;
var monthlyInsurance = homeInsuranceYearly / 12;
// Mortgage Factor (Principal & Interest per dollar borrowed)
var mortgageFactor = 0;
if (interestRate === 0) {
mortgageFactor = 1 / numPayments;
} else {
mortgageFactor = (monthlyRate * Math.pow(1 + monthlyRate, numPayments)) / (Math.pow(1 + monthlyRate, numPayments) – 1);
}
// Numerator and Denominator for V
var numerator = maxMonthlyPayment – monthlyInsurance + (downPayment * mortgageFactor);
var denominator = mortgageFactor + monthlyTaxRate;
var maxHomeValue = numerator / denominator;
// Edge case: if maxHomeValue < downPayment, it implies the income can't even support taxes/insurance
if (maxHomeValue < downPayment) {
// Technically they can buy a house = downpayment if taxes/insurance are low enough, but functionally 0 loan.
maxHomeValue = downPayment;
}
// Recalculate components based on calculated Home Value
var loanAmount = maxHomeValue – downPayment;
if (loanAmount (monthlyGrossIncome * 0.15)) {
document.getElementById("dtiWarning").style.display = "block";
}
}
// Initialize calculation on load
calculateAffordability();