This calculator helps you estimate how much house you can afford based on your income, debts, and estimated mortgage costs. Remember, this is an estimation and your actual borrowing power may vary based on lender specifics, credit score, and market conditions.
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.calculator-result {
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function calculateAffordability() {
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 propertyTaxRate = parseFloat(document.getElementById("propertyTaxRate").value);
var homeInsurance = parseFloat(document.getElementById("homeInsurance").value);
var resultDiv = document.getElementById("result");
if (isNaN(annualIncome) || isNaN(monthlyDebt) || isNaN(downPayment) || isNaN(interestRate) || isNaN(loanTerm) || isNaN(propertyTaxRate) || isNaN(homeInsurance)) {
resultDiv.innerHTML = "Error: Please enter valid numbers for all fields.";
return;
}
// Typically, lenders use a Debt-to-Income (DTI) ratio.
// A common guideline is that total housing costs (PITI) plus other monthly debts should not exceed 36%-43% of gross monthly income.
// Let's use 43% as a common upper limit for total debt, and assume P&I should be around 28% of gross monthly income for pre-qualification.
var grossMonthlyIncome = annualIncome / 12;
var maxTotalMonthlyDebt = grossMonthlyIncome * 0.43; // 43% DTI limit for total debt
var maxPitiPayment = maxTotalMonthlyDebt – monthlyDebt; // Maximum allowable PITI payment
if (maxPitiPayment <= 0) {
resultDiv.innerHTML = "Result: Based on your income and existing debts, it appears difficult to qualify for a new mortgage at this time. Consider increasing income or reducing debt.";
return;
}
var monthlyInterestRate = (interestRate / 100) / 12;
var numberOfPayments = loanTerm * 12;
// Calculate maximum loan amount based on max PITI payment
// Formula for P&I: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
// Rearranged to solve for P (Principal/Loan Amount): P = M * [ (1 + i)^n – 1] / [ i(1 + i)^n ]
// Where M = maxPitiPayment, i = monthlyInterestRate, n = numberOfPayments
var maxLoanAmount = 0;
if (monthlyInterestRate > 0) {
maxLoanAmount = maxPitiPayment * (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1) / (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments));
} else { // Handle 0% interest rate scenario (though unlikely for mortgages)
maxLoanAmount = maxPitiPayment * numberOfPayments;
}
// Now we need to work backwards to find the maximum *home price*
// Home Price = Loan Amount + Down Payment
// BUT, the property tax is based on home value, and insurance is a fixed cost.
// We need to estimate the monthly property tax and insurance.
// Estimated monthly property tax needs a HOME VALUE to be calculated. This is iterative or requires an assumption.
// A simpler approach: Assume property tax and insurance are part of the PITI calculation we just used.
// Let's refine maxPitiPayment to *exclude* property tax and insurance to better isolate P&I.
var monthlyInsurance = homeInsurance / 12;
// Property tax is tricky as it's % of home value. Let's make an initial estimate of home value to estimate P&I.
// A common strategy is to work backwards or make a reasonable assumption.
// Let's assume PITI is roughly 30-35% of gross monthly income for a slightly more conservative estimate on the housing portion itself.
// Or, we can try to estimate home value based on the loan amount *plus* down payment.
// Estimated Home Value = (Max Loan Amount if P&I was the only component) + Down Payment. This is circular.
// Let's try a different approach: Estimate the maximum affordable home price directly.
// Max Home Price = Max Loan Amount + Down Payment
// But Max Loan Amount is calculated based on P&I *plus* monthly taxes & insurance.
// Revised Approach: Calculate max monthly housing payment (PITI)
// Assume a typical split for PITI: P&I (75%), Taxes (15%), Insurance (10%) – these are rough estimates.
// This split can vary greatly, so this is a major simplification.
var totalMonthlyHousingBudget = grossMonthlyIncome * 0.35; // Let's target 35% of gross income for housing (PITI)
if (totalMonthlyHousingBudget <= monthlyDebt) {
resultDiv.innerHTML = "Result: Based on your income, your existing debt alone consumes too much of your income for housing payments. Consider reducing debt or increasing income.";
return;
}
var maxPitiPaymentBasedOnHousingBudget = totalMonthlyHousingBudget;
// Estimate Property Tax and Home Insurance based on a potential home price.
// This is a bit iterative, but we can start with an estimated home price.
// A common starting point: assume the loan amount is roughly 80% of the home value, and down payment is 20%.
var estimatedInitialHomeValue = (maxLoanAmount + downPayment); // This is not quite right.
// Let's try to isolate P&I from PITI.
// If PITI = P&I + Taxes + Insurance
// M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
// P = M * [ (1 + i)^n – 1] / [ i(1 + i)^n ]
// Let's assume taxes and insurance are a percentage of the *final affordable home price*.
// var HP be the Home Price.
// Monthly Tax = (HP * propertyTaxRate / 100) / 12
// Monthly Insurance = homeInsurance / 12
// Monthly P&I = maxPitiPayment – Monthly Tax – Monthly Insurance
// So, we need to solve for HP where:
// HP = Loan Amount + Down Payment
// Loan Amount = (maxPitiPayment – (HP * propertyTaxRate / 100) / 12 – homeInsurance / 12) * [ (1 + i)^n – 1] / [ i(1 + i)^n ]
// This is complex to solve directly. Let's use an approximation or an iterative approach.
// For simplicity, let's assume that maxPitiPayment (calculated from 43% DTI) is the TOTAL housing payment.
// We'll then BACK-CALCULATE the maximum home price.
// The max loan amount derived earlier was based on maxPitiPayment (43% DTI minus other debt).
// This maxPitiPayment *includes* property tax and insurance.
// We need to subtract estimated monthly taxes and insurance FROM this maxPitiPayment to get the maximum P&I payment.
// But the taxes depend on home value… this is where it gets tricky.
// Alternative Simplification: Estimate monthly P&I FIRST, then estimate Taxes and Insurance.
// Let's assume a lower threshold for housing costs as a percentage of income, say 30% for P&I only.
var maxMonthlyPI = grossMonthlyIncome * 0.30; // 30% of gross income for Principal & Interest
if (maxMonthlyPI <= 0) {
resultDiv.innerHTML = "Result: Your income is too low to afford any significant mortgage payment.";
return;
}
// Calculate max loan amount based on this max P&I payment
var maxLoanForPI = 0;
if (monthlyInterestRate > 0) {
maxLoanForPI = maxMonthlyPI * (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1) / (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments));
} else {
maxLoanForPI = maxMonthlyPI * numberOfPayments;
}
// Now, let's estimate the total affordable home price by adding the down payment
// And THEN calculate property tax and insurance based on this estimated home price.
// This is still an estimation because property tax is on the *home value*, not loan amount.
var affordableHomePriceEstimate = maxLoanForPI + downPayment;
var estimatedMonthlyPropertyTax = (affordableHomePriceEstimate * (propertyTaxRate / 100)) / 12;
var estimatedMonthlyInsurance = homeInsurance / 12;
var estimatedTotalMonthlyHousingCost = maxMonthlyPI + estimatedMonthlyPropertyTax + estimatedMonthlyInsurance;
// Check if this estimated total housing cost fits within the 43% DTI limit (including other debts)
if (estimatedTotalMonthlyHousingCost + monthlyDebt > maxTotalMonthlyDebt) {
// If it exceeds, we need to reduce the maxLoanForPI and thus the affordableHomePriceEstimate.
// This suggests a need for iteration or a more complex formula.
// For this calculator, let's adjust the initial assumption or provide a warning.
// Let's retry with a more integrated PITI calculation.
// We need to find Loan Amount (L) and Home Price (HP) such that:
// L = HP – Down Payment
// Monthly PITI = (L * monthlyInterestRate * (1 + monthlyInterestRate)^numberOfPayments) / ((1 + monthlyInterestRate)^numberOfPayments – 1) + (HP * propertyTaxRate / 100) / 12 + homeInsurance / 12
// And Monthly PITI + monthlyDebt <= grossMonthlyIncome * 0.43
// This is solved iteratively. Let's simplify by making an educated guess.
// Assume PITI is ~35% of gross monthly income.
var targetPiti = grossMonthlyIncome * 0.35;
// Try to find a HP that works. Let's guess HP and see.
var maxAffordableHP = 0;
var maxLoan = 0;
// Let's use a common rule of thumb: Max P&I is ~28% of gross monthly income.
var maxPIPayment = grossMonthlyIncome * 0.28;
if (maxPIPayment <= 0) {
resultDiv.innerHTML = "Result: Your income is insufficient to qualify for a mortgage.";
return;
}
// Calculate maximum loan based on this P&I limit.
var tempMaxLoan = 0;
if (monthlyInterestRate > 0) {
tempMaxLoan = maxPIPayment * (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1) / (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments));
} else {
tempMaxLoan = maxPIPayment * numberOfPayments;
}
// Now, consider the PITI payment which includes taxes and insurance.
// Let's use the 43% DTI limit as the ABSOLUTE maximum for PITI + Debt.
var maxTotalMonthlyObligation = grossMonthlyIncome * 0.43;
var maxPitiAllowed = maxTotalMonthlyObligation – monthlyDebt;
if (maxPitiAllowed <= 0) {
resultDiv.innerHTML = "Result: Your existing monthly debts are too high relative to your income to afford housing costs.";
return;
}
// We need to find a Home Price (HP) such that:
// Loan Amount (L) = HP – Down Payment
// Monthly P&I (calculated using L, interestRate, loanTerm) + Monthly Tax + Monthly Insurance 0) {
monthlyPIForPotentialLoan = tempMaxLoan * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1);
} else {
monthlyPIForPotentialLoan = tempMaxLoan / numberOfPayments; // very unlikely
}
var totalPitiForPotentialPrice = monthlyPIForPotentialLoan + monthlyTaxForPotentialPrice + monthlyInsuranceCost;
// Check against the max allowed PITI
if (totalPitiForPotentialPrice > maxPitiAllowed) {
// The estimated home price is too high. We need to calculate a more precise maximum loan.
// This indicates the P&I calculation alone was too generous and didn't account for taxes/insurance eating into that budget.
// Let's use maxPitiAllowed as the target for TOTAL PITI.
// We need to find Loan Amount (L) and Home Price (HP) where:
// L = HP – Down Payment
// P&I(L) + Tax(HP) + Insurance = maxPitiAllowed
// A simplified approach: Calculate the max LOAN amount that fits within the PITI budget.
// Assume taxes and insurance are roughly X% of the PITI budget. Let's use 25% for Taxes+Insurance.
var estimatedMonthlyTaxesAndInsurance = maxPitiAllowed * 0.25; // Rough estimate
var maxMonthlyPI_refined = maxPitiAllowed – estimatedMonthlyTaxesAndInsurance;
if (maxMonthlyPI_refined <= 0) {
resultDiv.innerHTML = "Result: Your income and debt levels do not allow for mortgage payments after accounting for estimated property taxes and insurance.";
return;
}
var refinedMaxLoan = 0;
if (monthlyInterestRate > 0) {
refinedMaxLoan = maxMonthlyPI_refined * (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1) / (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments));
} else {
refinedMaxLoan = maxMonthlyPI_refined * numberOfPayments;
}
// The maximum affordable home price is then this refined max loan + down payment.
var finalAffordableHomePrice = refinedMaxLoan + downPayment;
// Recalculate PITI for this final price to confirm.
var finalMonthlyTax = (finalAffordableHomePrice * (propertyTaxRate / 100)) / 12;
var finalMonthlyInsurance = homeInsurance / 12;
var finalMonthlyPI = 0;
if (monthlyInterestRate > 0) {
finalMonthlyPI = refinedMaxLoan * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1);
} else {
finalMonthlyPI = refinedMaxLoan / numberOfPayments;
}
var finalTotalPiti = finalMonthlyPI + finalMonthlyTax + finalMonthlyInsurance;
// Final check: is this finalTotalPiti within budget?
if (finalTotalPiti > maxPitiAllowed) {
// This can happen if the initial 25% estimate for taxes/insurance was too low.
// For this calculator, we'll state the limitation.
resultDiv.innerHTML = "Result: Could not precisely determine affordability due to variable tax/insurance costs. However, based on estimates, your maximum estimated home price is approximately $" + Math.round(finalAffordableHomePrice).toLocaleString() + ". Please consult a mortgage professional.";
return;
}
maxLoan = refinedMaxLoan;
maxAffordableHP = finalAffordableHomePrice;
} else {
// The initial estimate using P&I as 28% of income worked well enough and fit PITI budget.
maxLoanAmount = tempMaxLoan;
maxAffordableHP = potentialHomePrice;
}
resultDiv.innerHTML = "Based on the information provided, your estimated maximum affordable home price is: $" + Math.round(maxAffordableHP).toLocaleString() + "." +
"This includes a down payment of $" + downPayment.toLocaleString() + ", allowing for a mortgage of approximately $" + Math.round(maxAffordableHP – downPayment).toLocaleString() + "." +
"Estimated total monthly housing costs (PITI): $" + Math.round(totalPitiForPotentialPrice).toLocaleString() + "" +
"(Based on a 43% Debt-to-Income ratio and assuming P&I is approx 28% of gross monthly income)";
} else {
// The first estimate worked. P&I alone (28% of income) leads to a home price that fits within the 43% DTI.
var estimatedHomePrice = maxLoanAmount + downPayment;
var estimatedMonthlyPropertyTax = (estimatedHomePrice * (propertyTaxRate / 100)) / 12;
var estimatedMonthlyInsurance = homeInsurance / 12;
var estimatedMonthlyPI = 0;
if (monthlyInterestRate > 0) {
estimatedMonthlyPI = maxLoanAmount * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1);
} else {
estimatedMonthlyPI = maxLoanAmount / numberOfPayments;
}
var totalMonthlyHousingCosts = estimatedMonthlyPI + estimatedMonthlyPropertyTax + estimatedMonthlyInsurance;
resultDiv.innerHTML = "Based on the information provided, your estimated maximum affordable home price is: $" + Math.round(estimatedHomePrice).toLocaleString() + "." +
"This includes a down payment of $" + downPayment.toLocaleString() + ", allowing for a mortgage of approximately $" + Math.round(maxLoanAmount).toLocaleString() + "." +
"Estimated total monthly housing costs (PITI): $" + Math.round(totalMonthlyHousingCosts).toLocaleString() + "" +
"(Based on a 43% Debt-to-Income ratio and assuming P&I is approx 28% of gross monthly income)";
}
}