Before you fall in love with a home, the more useful question is how much home your income can actually carry. This mortgage affordability calculator works backward from what a lender will approve: it takes your annual income, your existing monthly debts, the cash you have for a down payment, the rate you expect to lock, and the debt-to-income ratio (DTI) you are comfortable with, then solves for the largest monthly payment, the largest loan, and the largest home price you can take on without straining your budget.
Unlike a regular mortgage calculator that starts from a home price and tells you the payment, this tool starts from your paycheck and tells you the price ceiling. Slide any input and the result card updates instantly, so you can see how adding a student-loan payment, waiting for a rate to drop, or saving a bigger down payment moves the number.
How to Use
- Enter your Annual Gross Income — your household pre-tax income, including salary, wages, and any other steady income a lender will count. Do not use take-home pay; underwriters use gross.
- Fill in Existing Monthly Debts — car loans, student loans, credit-card minimums, alimony, and any other recurring payment that shows up on your credit report. Do not include rent, utilities, or groceries.
- Set your Down Payment in dollars. The more you put down, the less you need to borrow, but also the more cash you tie up at closing. Twenty percent is the classic threshold that removes private mortgage insurance.
- Type the Interest Rate (APR) you expect. If you have not locked a rate yet, plug in today's national average for your credit profile, then test +/- 0.5% to stress-test the budget.
- Pick the Loan Term — 30 years is the default, but a 15-year term at a lower rate reduces the loan amount a lender will offer even as it lowers your lifetime interest.
- Adjust the Max Debt-to-Income Ratio (DTI). Most conventional loans cap total monthly debt at around 36% of gross income, though FHA and other programs can go higher. A lower cap is a safer personal rule.
- Optionally add Est. Monthly Property Tax, Est. Monthly Home Insurance, and Est. Monthly PMI. These come out of the same DTI budget, so entering them gives you a far more honest ceiling.
The result card shows your monthly gross income, the total monthly debt your DTI cap allows, the slice left for housing (PITI), the slice left for pure principal and interest, and — the two headline numbers — the max mortgage loan and the max home price you can afford.
The Affordability Formula, Step by Step
Lenders do not look at your income in isolation; they look at how much of it already goes to debt. The engine runs four steps:
- Monthly gross income = annual income / 12.
- Maximum total monthly debt allowed = monthly gross income x your DTI cap. For a $120,000 household at 36%, that is $3,600 per month.
- Maximum housing payment (PITI) = that cap minus your existing debts. With $500 of car and student loans, only $3,100 remains for the mortgage, tax, insurance, and PMI combined.
- Maximum loan amount is then back-solved from the standard amortization formula. If M is the monthly payment, r the monthly rate, and n the number of payments, the loan P is:
P = M / [ r(1 + r)ⁿ / ((1 + r)ⁿ − 1) ]
At 7.0% for 30 years, the payment factor is about 0.006653. A $3,100 monthly principal-and-interest budget therefore supports a loan of roughly $466,000. Adding your $60,000 down payment puts the maximum home price at about $526,000. That is the number to shop with.
Why the Back-End DTI Rule Matters
The 36% back-end rule of thumb comes from decades of default data: borrowers spending more than about a third of their gross income on debt consistently struggle when rates rise or incomes dip. Breaking it down:
- Front-end (housing-only) ratio — PITI as a share of gross income. Lenders usually want this near 28%.
- Back-end (total) ratio — PITI plus all other debts. The 36% cap is the back-end version.
- Qualifying vs. comfortable — a lender may approve you at 43% or even 50% with compensating factors, but that does not mean you should stretch to the edge. The calculator lets you set your own cap; choosing 30% instead of 36% will produce a lower, safer price ceiling.
If your rate is 0%, the formula divides by zero, so the engine simply assumes the loan principal is repaid in equal monthly chunks — the same result you would get with an interest-free loan.
Examples
Example 1 — Standard profile. A household earns $120,000 a year, pays $500 a month toward a car loan and a student loan, has $60,000 saved for down payment, expects a 7.0% rate on a 30-year loan, and holds a 36% DTI cap. Monthly gross is $10,000; the DTI cap allows $3,600 of total debt; subtracting the $500 existing payment leaves $3,100 for housing. Back-solving the PMT factor gives a max loan of about $466,000 and a max home price of about $526,000.
Example 2 — Zero existing debt. The same $120,000 income but no car or student payment unlocks the full $3,600 for housing. At 7.0% for 30 years, that supports a loan of about $541,000, or $601,000 with the same $60,000 down. Paying off a small car loan before you apply can add tens of thousands to your buying power.
Example 3 — High-income, high-price market. A household earning $1,000,000 a year with $2,000 of monthly debts and $200,000 down, at 6.5% on a 30-year loan. The DTI cap allows $30,000 of total monthly debt; after existing debts, $28,000 is free for housing. That supports a loan of about $4,430,000 and a max home price near $4,630,000 — useful for sanity-checking a jumbo-loan budget before you shop.
Example 4 — 15-year term. Keep the $120,000 income, $500 debts, $60,000 down, but switch to a 15-year loan at 6.0%. The same $3,100 housing budget now amortizes twice as fast, supporting a loan of only about $367,000 and a home price near $427,000. The 15-year route costs you buying power today but saves a fortune in interest.
FAQ
How much mortgage can I afford on my salary?
As a rule of thumb, lenders look for your total monthly debt — including the new mortgage — to stay under roughly 36% of your gross monthly income. Divide your annual salary by 12, multiply by 0.36, subtract your existing monthly debts, and you have the monthly budget for PITI. Plug that number into the calculator above and it back-solves the max loan and home price.
What is the difference between front-end and back-end DTI?
The front-end ratio counts only housing costs — principal, interest, taxes, insurance, and PMI — as a share of gross income, typically capped near 28%. The back-end ratio adds car loans, student loans, credit-card minimums, and other recurring debts, typically capped near 36%. This calculator uses the back-end ratio because it is the stricter and more commonly underwritten test.
How much down payment do I actually need?
Conventional loans accept as little as 3%–5% down, but you will pay private mortgage insurance until you reach 20% equity. FHA loans go as low as 3.5%. Putting 20% down removes PMI, qualifies you for a better rate, and lowers the loan amount — but tying up more cash at closing can leave you with no emergency fund. The calculator lets you test different down-payment amounts in dollars.
Does a higher credit score change what I can afford?
Indirectly, yes. Better credit usually earns you a lower interest rate, and a lower rate means each dollar of monthly payment supports a larger loan. On a $3,100 monthly budget, dropping the rate from 7.5% to 6.5% can add roughly $30,000–$40,000 to the loan size. Improve your score before applying, then re-run the calculator with the new rate.
Should I trust the lender's approval amount?
Treat an approval as a ceiling, not a target. A lender may qualify you at a 43%–50% DTI because their model is optimizing for repayment, not for your comfort or savings goals. Most homeowners who feel house-poor borrowed close to their approved limit. Running this calculator with a 30%–36% cap gives you a budget you can actually live with.
How do property taxes and insurance affect affordability?
They come straight out of the same DTI budget. A $250,000 home in a high-tax state can carry $400–$600 a month in property tax plus another $100–$200 in insurance. Entering those lines in the advanced section reduces your max loan dollar-for-dollar, which is why two buyers with identical incomes can afford very different homes depending on the county they shop in.
Disclaimer
This mortgage affordability calculator is provided for informational purposes only and does not constitute financial, lending, tax, or investment advice. Estimates are based on the DTI rule and the standard amortization formula; actual loan offers vary by lender, credit profile, down payment, location, property type, and loan program. Property tax, insurance, and PMI figures you enter are assumptions, not quotes. Always confirm your final approval, rate, and terms directly with a licensed mortgage professional before making an offer or committing to a loan.