To determine home affordability, apply the 28/36 debt-to-income rule to your gross monthly income and existing monthly debts: housing costs should stay under 28% of income, and total recurring debt (including the future mortgage) under 36% of income. The smaller of those two numbers becomes your maximum monthly housing payment. That payment is then converted into a maximum loan through inverse amortization, and adding your down payment produces the highest home price in your realistic range. Doing this by hand requires two formulas — the 28/36 ceilings and the annuity present-value equation — and is easy to miscalculate when interest rates shift or debts change. The Home Affordability Calculator automates this process in your browser. You enter your gross income, your recurring monthly debts, your down payment, your expected interest rate, and your loan term, and it instantly returns three numbers: the maximum home price, the maximum loan amount, and the maximum monthly payment that fits your budget. The result recalculates the moment you change any input, so you can compare terms or simulate paying down a debt without leaving the page. Every computation runs locally — nothing you type is uploaded or saved.
The 28/36 Rule and the Two Ceilings It Sets
Lenders do not approve loans based on the price of the house — they approve them based on the monthly payment's share of your income. The 28/36 rule encodes that idea as two ceilings, both expressed as percentages of your gross monthly income (income before taxes and deductions). The front-end ratio caps housing costs — in this calculator, principal and interest on the loan — at 28%. The back-end ratio caps all recurring debt, including the future mortgage plus car loans, student loans, and minimum credit-card payments, at 36%. The calculator uses the smaller of those two numbers as your maximum monthly housing budget, so the formula is:
Max housing payment = min(0.28 × income, 0.36 × income − monthly debts)
When your other debts are small, the 28% front-end ratio usually binds and you can spend the full 28% on housing. When your other debts are large, the back-end ratio pulls the ceiling down. If your existing debts already exceed 36% of your gross income on their own, the formula returns zero — meaning no room for a mortgage payment under this rule.
For a concrete illustration, take a household earning $7,000 per month gross with $500 in monthly debts (a car loan and a student-loan minimum, for instance). The front-end ceiling is 0.28 × $7,000 = $1,960. The back-end ceiling is 0.36 × $7,000 − $500 = $2,520 − $500 = $2,020. Because $1,960 is the smaller number, the maximum monthly housing budget is $1,960. That $1,960 is the input that the calculator then runs through inverse amortization to find the largest loan your budget can support. The 28/36 rule is widely cited by lenders and covered in detail by both the Wikipedia article on debt-to-income ratio and the Consumer Financial Protection Bureau.
What Goes Into Your Affordability Number
Five inputs drive the result, and each one moves the answer in a predictable direction.
- Gross income. Higher gross income raises both the 28% and the 36% ceilings. Enter it as either a monthly or annual figure — the calculator converts annual to monthly internally.
- Recurring monthly debts. Car loans, student loans, and credit-card minimums reduce the back-end ceiling dollar-for-dollar. They do not affect the 28% front-end ceiling.
- Down payment. A larger cash down payment shrinks the loan you need to borrow. Because the maximum monthly payment is fixed by the 28/36 rule, every extra dollar you put down expands the home price you can target.
- Annual interest rate. A higher rate means each monthly payment buys less of the loan's principal, so the maximum loan — and home price — falls. A lower rate stretches the same payment further.
- Loan term. A longer term (for example, 30 years instead of 15) spreads the same total interest and principal across more months, so each monthly payment is smaller and the maximum loan is larger. Shorter terms produce larger monthly payments and smaller maximum loans.
How to Determine Your Home Affordability
Once you have your numbers in front of you, the calculation takes three inputs and an instant readout.
- Enter your gross income and choose whether it is monthly or annual, then add your total recurring monthly debt payments. Include car loans, student loans, and credit-card minimums — but skip discretionary spending like subscriptions or groceries.
- Enter the cash down payment you plan to make, your expected annual interest rate, and the loan term in years. The down payment is the cash you bring to closing, not the total price. The interest rate can be a current quote or a what-if value for stress-testing.
- Read the affordable home price, affordable loan amount, and maximum monthly housing payment. All three figures recalculate instantly under the 28/36 rule every time you change an input, so you can adjust the down payment, rate, or term and watch the home price respond.
Open the Home Affordability Calculator directly to run these steps on your own numbers.
Affordability vs. Mortgage Calculator: A Side-by-Side Look
The two calculators answer opposite questions, and using the wrong one leads to a number that does not match your situation. The table below shows what each tool takes as input and what it returns.
| Feature | Home Affordability Calculator | Mortgage Calculator |
|---|---|---|
| Primary question | How much house can I afford? | What is the monthly payment on this loan? |
| Starting point | Your income and existing debts | The loan amount and interest rate |
| Key inputs | Gross income, monthly debts, down payment, interest rate, loan term | Loan amount, interest rate, loan term, down payment |
| Main output | Maximum affordable home price and loan amount | Monthly principal-and-interest payment |
| Rule applied | 28/36 debt-to-income ceiling | Standard amortization formula |
| Best used when | You are starting your home search and want a realistic price range | You have a specific property or loan offer and want to see the payment |
In short, the affordability calculator looks backward from your budget to find the right price, while a mortgage calculator looks forward from a price to find the right payment. For a complete walk-through of how those numbers feed into an actual loan, the Mortgage Calculator picks up where this one leaves off.
Inputs That Quietly Reshape Your Budget
The 28/36 ceiling sets a hard line, but several levers inside that line let you stretch the same income into a different home price.
- Paying down a car loan or student loan. Each $100 removed from monthly debts raises the back-end ceiling by $100, which can lift the maximum housing payment and therefore the affordable price.
- Larger down payment. Since the maximum loan is fixed by the 28/36 payment, every extra dollar down adds a dollar to the top-line home price you can target — without changing your monthly payment.
- Choosing a 30-year term over a 15-year term. A longer term lowers each monthly payment, so the same 28/36 ceiling supports a larger loan. The trade-off is substantially more interest paid over the life of the loan.
- Improving your credit score before applying. Better credit typically unlocks a lower interest rate, and the affordability calculator will reflect that immediately when you adjust the rate field.
- Adding a co-borrower's income. If a partner, spouse, or family member will be on the loan, combine gross incomes to widen both the 28% and 36% ceilings proportionally.
What the Estimate Leaves Out
The number you see is a principal-and-interest ceiling, not a complete monthly-cost ceiling. Several recurring costs typically sit on top of the mortgage payment and reduce the price you can comfortably carry:
- Property taxes. Collected monthly with most mortgage payments and held in escrow.
- Homeowners insurance. Usually required by the lender and escrowed alongside taxes.
- HOA or condominium fees. Common in townhomes, condos, and planned communities.
- Private mortgage insurance (PMI). Generally required when the down payment is below 20% of the home price.
Add those expenses to the maximum monthly housing payment to see what your true housing budget looks like — and confirm the actual numbers with a licensed mortgage professional before making an offer. The 28/36 rule is a widely used guideline, but real underwriting also weighs your credit score, cash reserves, employment history, and the specific loan program (FHA, VA, and conventional loans each use different limits, and some lenders stretch ratios higher). Use the calculator's output as a starting benchmark for your search, then verify with a lender.