The home affordability calculator works in three steps: you enter your gross income and existing monthly debts, then your down payment and loan terms, and the tool returns the maximum home price, loan amount, and monthly housing payment that the 28/36 debt-to-income rule allows for your situation. Instead of starting with a loan amount and computing a payment forward, the tool works in reverse — it begins with what you can actually carry each month, runs that ceiling through an inverse loan formula at your rate and term, and finds the largest loan that monthly payment can support. The 28/36 rule is a lender guideline that caps housing costs at 28% of your gross monthly income (the front-end ratio) and total recurring debt at 36% (the back-end ratio); the calculator picks the smaller of the two ceilings. When your other debts are small, the 28% front-end ratio usually binds; when debts are heavy, the 36% back-end ratio pulls the number down. Every value is processed in your browser, nothing you type is uploaded or stored, and adjusting any input recalculates the result instantly so you can compare trade-offs as you go.
What to Gather Before You Open the Calculator
Before you load the tool, gather five numbers so your first run gives you a usable result rather than a guess.
- Gross income. Your total pay before taxes and deductions. If you have a co-borrower, use the combined gross income for both of you.
- Monthly recurring debts. The sum of minimum monthly totals for car loans, student loans, credit-card minimums, personal loans, child support, and any other installment debt. Skip utilities, groceries, and subscriptions — only debt with a set monthly payment counts under the 28/36 rule.
- Cash down payment. How much cash you can put toward the purchase. The calculator adds this directly to your maximum loan to give the top home price.
- Expected interest rate. Pull one or two online rate quotes before you start so the rate field is realistic rather than round.
- Loan term. 30 years is most common, but 15- and 20-year terms are worth comparing if you want lower total interest.
With these numbers on a single page, your first pass through the calculator takes about a minute.
The Three-Step Workflow in the Calculator
The tool is built around three input groups and three output numbers, and every change you make recalculates the outputs instantly.
- Income and debts (the first input group).
- Down payment, interest rate, and loan term (the second input group).
- Outputs: affordable home price, affordable loan amount, and maximum monthly housing payment.
Knowing this layout before you start lets you run scenarios — a bigger down payment, a shorter term, paid-off debts — by changing one field at a time and watching the outputs shift. The instant recalculation is the part most first-time users underestimate: instead of running the tool once and trusting the first number, you can probe it like a spreadsheet.
Enter Income, Debts, and Down Payment
In the first input group, type your gross income and choose whether the number is monthly or annual from the toggle. If you know only your annual salary, pick annual; if you think in monthly paychecks, pick monthly. The calculator handles the conversion internally. Below that, enter the total of your recurring monthly debt payments — the sum of car, student, credit-card minimums, and any other installment debt. The calculator uses this number to test whether the 36% back-end ratio will bind tighter than the 28% front-end ratio for your situation.
Next, enter the cash down payment you plan to make. A larger down payment directly raises the affordable home price because it is added on top of the maximum loan the inverse formula produces. A common rule of thumb is 20% down to avoid private mortgage insurance, but the tool accepts any amount from zero upward. Every dollar you add to the down payment is a dollar added to the affordable home price, with no other effect on the formula — which is why down payment is the most linear lever on the result.
Set the Rate and Loan Term
In the second input group, type your expected annual interest rate as a percentage — 6.5, not 0.065. Use the rate a lender has quoted you if you have one; if not, use a current national average so the result reflects realistic numbers. Then enter the loan term in years. Thirty is standard; fifteen and twenty are common alternatives that trade a higher monthly payment for much lower total interest over the life of the loan.
Rate and term work together through the inverse amortization formula. A lower rate stretches each dollar of monthly payment further, raising the loan amount. A shorter term shrinks the loan amount because the payment has to amortize a balance over fewer months. Net effect: dropping your rate usually raises the affordable home price; shortening the term usually lowers it. The combined effect is rarely intuitive on a first pass, so try both levers in the same session.
Read the Three Numbers the Calculator Returns
The calculator displays three outputs that update as you type:
- Affordable home price — the top of your realistic search range. This is your maximum loan plus your down payment.
- Affordable loan amount — the largest mortgage your maximum monthly payment can support at the rate and term you entered.
- Maximum monthly housing payment — the smaller of 28% of your gross monthly income and 36% of your gross monthly income minus your other debts. This single number drives everything else.
The maximum monthly housing payment is the number that anchors the others. It comes straight from the 28/36 rule, with no interest-rate or term dependency baked in. Both the loan amount and the home price are derived from this ceiling plus your loan terms, which is why two people with identical incomes but different rates can carry very different loan amounts. If your debts are low, the 28% front-end ratio usually produces the payment. If your debts are high, the 36% back-end ratio produces a smaller number and your search range drops accordingly. If your debts are very high, the budget can collapse to zero — a clear signal that paying down existing debt is the next move.
Get Started: A Walkthrough of Each Step
- Open the Home Affordability Calculator on this site.
- In the first input row, type your gross income and choose monthly or annual.
- Add the sum of your recurring monthly debt payments in the debts field.
- Type your planned cash down payment in the down payment field.
- Enter your expected annual interest rate as a percentage.
- Enter the loan term in years — 30, 20, or 15 are the most common choices.
- Read the three output numbers: affordable home price, affordable loan amount, and maximum monthly housing payment.
- Adjust any input to compare scenarios — a bigger down payment, a shorter term, or a paid-off car loan — and watch the outputs change in real time.
What the 28/36 Rule Means for Your Number
The 28/36 rule sets two ceilings on what you can carry each month. The front-end ratio limits housing costs — principal and interest — to 28% of gross monthly income. The back-end ratio limits total recurring debt, which is your future mortgage plus car loans, student loans, and credit-card minimums, to 36% of gross income. The Consumer Financial Protection Bureau describes these as the two standard benchmarks lenders use to judge whether a new housing payment fits inside a borrower's overall debt load.
The calculator applies both ratios and keeps the smaller number, then converts that monthly ceiling into a maximum loan using the annuity present-value formula. With r equal to your annual rate divided by 12, and n equal to years multiplied by 12:
Max monthly housing = min(0.28 × income, 0.36 × income − monthly debts), clamped to at least 0.
Max loan = payment × [(1 + r)n − 1] / [r × (1 + r)n], or payment × n when r = 0.
Affordable home price = max loan + down payment.
The result is principal and interest only — no taxes, insurance, HOA, or PMI — and the rate is treated as fixed over the full term. The ceiling is clamped to zero, so a heavy debt load produces an honest zero rather than a negative number.
A Worked Example With $80,000 Income
Suppose your gross income is $80,000 per year, your recurring monthly debts total $200, your down payment is $20,000, your expected rate is 6.0%, and you want a 30-year term.
Step 1 — Monthly income: $80,000 ÷ 12 = $6,666.67.
Step 2 — Front-end ceiling: 0.28 × $6,666.67 = $1,866.67.
Step 3 — Back-end ceiling: 0.36 × $6,666.67 − $200 = $2,400 − $200 = $2,200.
Step 4 — Pick the smaller of the two: min($1,866.67, $2,200) = $1,866.67. The 28% front-end ratio binds because your other debts are small.
Step 5 — Translate the payment into a loan. With r = 0.06 ÷ 12 = 0.005 and n = 30 × 12 = 360 months, the inverse amortization formula yields a maximum loan of approximately $311,300.
Step 6 — Add the down payment: $311,300 + $20,000 ≈ $331,300.
If your debts rose to $1,000 per month, the back-end ceiling would drop to $1,400 — about three-quarters of the front-end number — and your affordable home price would fall by roughly 25%. That sensitivity is the single most useful thing to notice on your first run: paying off a monthly obligation before you shop has a larger effect than a small rate change or a slightly bigger down payment.
How Sensitive the Output Is to Each Input
On a first run, it helps to know which inputs move the result most. The max monthly housing payment is set entirely by income and debts — rate and term do not enter it at all. The loan amount depends on the rate, the term, and that payment together. The affordable home price depends on the loan amount plus the down payment.
| Input change | Direction of affordable home price | Why |
|---|---|---|
| Higher gross income | Up | Raises the 28/36 ceiling directly |
| Larger monthly debts | Down (sometimes to zero) | Shrinks the 36% back-end ceiling |
| Bigger cash down payment | Up | Added on top of the max loan |
| Lower interest rate | Up | Stretches the payment further via inverse amortization |
| Longer loan term (e.g., 30 vs. 15) | Up, more total interest | Spreads the same payment over more months |
| Shorter loan term | Down, less total interest | Fewer months to amortize the balance |
When you compare two scenarios, change only one input at a time so you can attribute the movement. Changing three inputs at once produces a result, but it hides which decision actually drove it.
What to Do With the Result — and What It Doesn't Include
The number you get is a starting benchmark, not a final approval. The estimate covers loan principal and interest only; property taxes, homeowners insurance, HOA dues, and private mortgage insurance will all add to your true monthly cost and lower the home price you can comfortably carry. Some loan programs — FHA, VA, and conventional — use different DTI limits, and some lenders stretch ratios higher than 28/36, so the figure is a widely used guideline rather than a guarantee. Real underwriting also weighs your credit score, cash reserves, employment history, and the specifics of the property.
Treat the result as the top of a realistic search range. Once you have a specific listing in mind, run the same numbers through a mortgage calculator to see what the payment would be at that exact loan amount, and confirm the final figures with a licensed mortgage professional before you make an offer. For a deeper walk-through of how debts and other inputs shape the number, see How Existing Debts Cut Into Your Home Affordability.
If you're weighing options, Confirm Home Affordability Calculator by Income Numbers covers this in detail.