Determining how much house you can afford is a crucial step in the home-buying process.
The Mortgage Affordability Calculator helps you estimate the maximum mortgage loan amount you
might qualify for, based on your income, existing debt, down payment, and prevailing interest rates.
Key Factors Influencing Affordability:
Annual Household Income: This is the primary driver of how much lenders believe you can repay.
Higher income generally translates to a higher borrowing capacity.
Total Monthly Debt Payments: Lenders look at your debt-to-income ratio (DTI).
This includes car loans, student loans, credit card payments, and any other recurring debts.
Lower existing debt means more room for a mortgage payment.
Down Payment: A larger down payment reduces the amount you need to borrow,
lowering your Loan-to-Value (LTV) ratio. It can also improve your chances of loan approval
and potentially secure better interest rates.
Interest Rate: Even small variations in interest rates can significantly impact
your monthly payment and the total interest paid over the life of the loan. Higher rates
reduce affordability.
Loan Term: The duration of your mortgage (e.g., 15, 30 years) affects your monthly
payments. Shorter terms usually have higher monthly payments but less total interest paid.
Longer terms have lower monthly payments but more total interest.
This calculator uses common lending guidelines, such as the 28/36 rule, as a starting point.
The 28% rule suggests that your total housing expenses (principal, interest, taxes, insurance – PITI)
should not exceed 28% of your gross monthly income. The 36% rule states that all your monthly debt payments,
including your potential mortgage, should not exceed 36% of your gross monthly income.
Your actual borrowing capacity may vary based on lender-specific criteria, credit score, and other financial
factors. It's always recommended to speak with a mortgage lender for a pre-approval.
How it Works:
Calculate Gross Monthly Income: Your annual income is divided by 12.
Determine Maximum Housing Payment: Typically, 28% of your gross monthly income is used as an upper limit for PITI.
Calculate Maximum Total Debt Payment: Typically, 36% of your gross monthly income is the ceiling for all your monthly debts.
Determine Allowable Mortgage Payment: Subtract your existing monthly debt payments from the maximum total debt payment allowed. This gives you the maximum you can allocate to your mortgage payment (PITI).
Estimate Loan Amount: Using the allowable mortgage payment, interest rate, and loan term, the calculator estimates the maximum loan amount you could take. This involves using a mortgage payment formula in reverse.
Add Down Payment: The estimated loan amount is added to your down payment to suggest a maximum home price you might be able to afford.
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function calculateMortgageAffordability() {
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 loanTerm = parseFloat(document.getElementById("loanTerm").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
if (isNaN(annualIncome) || isNaN(monthlyDebt) || isNaN(downPayment) || isNaN(interestRate) || isNaN(loanTerm) ||
annualIncome < 0 || monthlyDebt < 0 || downPayment < 0 || interestRate < 0 || loanTerm <= 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for all fields.";
return;
}
// — Standard Lending Guidelines (28/36 Rule) —
var grossMonthlyIncome = annualIncome / 12;
// Rule 1: Housing expenses (PITI) shouldn't exceed 28% of gross monthly income
var maxPITI = grossMonthlyIncome * 0.28;
// Rule 2: Total debt payments (including estimated mortgage PITI) shouldn't exceed 36% of gross monthly income
var maxTotalDebt = grossMonthlyIncome * 0.36;
var maxMortgagePaymentOnly = maxTotalDebt – monthlyDebt;
// The more conservative limit for the PITI payment
var affordablePITI = Math.min(maxPITI, maxMortgagePaymentOnly);
if (affordablePITI 0 && numberOfPayments > 0) {
var numerator = monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments);
var denominator = Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1;
var factor = numerator / denominator;
if (factor > 0) {
estimatedMaxLoanAmount = estimatedMonthlyPI / factor;
}
} else if (monthlyInterestRate === 0 && numberOfPayments > 0) {
// Handle 0% interest rate case (though uncommon for mortgages)
estimatedMaxLoanAmount = estimatedMonthlyPI * numberOfPayments;
}
var estimatedMaxHomePrice = estimatedMaxLoanAmount + downPayment;
// Add a buffer for taxes and insurance for a more realistic PITI figure
// Assuming Taxes + Insurance ~ 1.2% of home value annually / 12 months
var estimatedMonthlyTaxesAndInsurance = (estimatedMaxHomePrice * 0.012) / 12;
var actualEstimatedPITI = estimatedMaxLoanAmount + estimatedMonthlyTaxesAndInsurance;
// Recalculate if the initial estimate exceeds affordablePITI
if (actualEstimatedPITI > affordablePITI && estimatedMaxLoanAmount > 0) {
// We overshot, need to reduce the loan amount to fit within affordablePITI
// This is a simplified iterative or direct calculation adjustment.
// A more precise method is solving PITI = PI_portion + TaxIns_portion where TaxIns_portion depends on Home Price.
// Home Price = Loan + Down Payment. TaxIns = (Loan+Down) * 0.012 / 12
// PITI = PI_calc(Loan) + (Loan+Down) * 0.012 / 12
// We know PITI 0) {
var numeratorAdj = affordablePITI – (downPayment * 0.001);
var denominatorAdj = factor + 0.001;
if (denominatorAdj > 0) {
adjustedLoanAmount = numeratorAdj / denominatorAdj;
}
}
if (adjustedLoanAmount > 0) {
estimatedMaxLoanAmount = adjustedLoanAmount;
estimatedMaxHomePrice = estimatedMaxLoanAmount + downPayment;
} else {
// If adjustment fails, it means even with maximum effort, affordability is constrained
estimatedMaxLoanAmount = 0;
estimatedMaxHomePrice = downPayment;
}
}
if (estimatedMaxHomePrice > 0) {
resultDiv.innerHTML =
"Estimated Maximum Mortgage Loan: $" + estimatedMaxLoanAmount.toLocaleString(undefined, { minimumFractionDigits: 0, maximumFractionDigits: 0 }) + "" +
"Estimated Maximum Home Price: $" + estimatedMaxHomePrice.toLocaleString(undefined, { minimumFractionDigits: 0, maximumFractionDigits: 0 }) + "";
} else {
resultDiv.innerHTML = "Based on your inputs, affordability is very limited. Please consult a mortgage professional.";
}
}