Mortgage Affordability Calculator

How Much House Can You Afford?

The question most home buyers ask is "how much will the bank lend me?" That is the wrong question. What you can be approved to borrow and what you can comfortably afford to repay are different numbers — often very different. Lenders operate on their own risk models, which include your income, debts, and credit score. They do not know your full financial picture: your emergency fund, your childcare costs, whether you plan to have kids, your job stability, or whether you have aging parents who may need financial help.

The right approach is budget-first, then search. Determine the maximum monthly housing payment you can absorb without financial strain, back-calculate the home price that corresponds to that payment, and only then begin looking at listings in that price range. Most buyers do the opposite: they fall in love with a home, then scramble to find a mortgage that fits — a sequence that predictably leads to stretching further than is prudent.

This calculator uses the 28/36 rule — the conventional lending guideline developed by Fannie Mae and Freddie Mac that has been the foundation of US mortgage underwriting for decades. It applies your specific income, existing debt payments, and down payment to find the maximum home price at which your housing costs stay within both limits. The result is your budget ceiling, not your spending target.

The 28/36 Rule: How Lenders Measure Affordability

The 28/36 rule defines two debt-to-income ratio limits that apply simultaneously. Your home budget is constrained by whichever limit binds first.

The front-end ratio (28%) caps your monthly housing costs at 28% of your gross monthly income. Housing costs in this context means the full PITI payment: principal, interest, property taxes, homeowners insurance, and PMI (if applicable). It does not include utilities, maintenance, or HOA fees. For someone earning $80,000 per year ($6,667/month), the front-end limit is $1,867 per month.

The back-end ratio (36%) caps your total monthly debt obligations at 36% of gross monthly income. This includes the proposed housing payment plus all recurring debt payments: car loans, student loans, minimum credit card payments, personal loans, and any other installment debt. The same $80,000 earner has a back-end limit of $2,400. If they have $500 in existing monthly debt payments, only $1,900 is available for housing — slightly more than the front-end limit in this case, meaning the front-end ratio is the binding constraint.

In practice, front-end constrains buyers with minimal debt and back-end constrains those with significant existing obligations. The more debt you carry, the more the back-end ratio shrinks your housing budget. Each dollar of monthly debt payment reduces your maximum housing budget by exactly one dollar — which translates to roughly $125–$150 less in home-buying power per dollar of monthly debt at today's typical rates.

One important note: some lenders will approve borrowers at back-end ratios up to 43–50% with strong compensating factors — high credit scores (740+), large down payments (20%+), or substantial cash reserves after closing. Getting approved at 45% DTI does not mean you will be financially comfortable at that level. The 36% back-end guideline represents a standard at which most buyers retain enough financial flexibility for emergencies, maintenance, and retirement contributions.

PITI: What Is Really in Your Monthly Payment

The monthly mortgage payment quoted by lenders is often just the principal and interest (P&I) — the amortized loan payment calculated from the loan amount, rate, and term. But your actual housing cost includes three or four additional components. The gap between the P&I figure and the total PITI payment is frequently where buyers are surprised.

Principal. On a 30-year loan, very little of your early monthly payment goes toward principal. In year one at 7%, roughly 20% of each payment reduces the loan balance; 80% goes to interest. This is the normal amortization pattern — the principal share grows gradually over the life of the loan as the outstanding balance shrinks. On a $210,000 loan at 7%, the first payment of $1,397 contains only about $172 of principal reduction and $1,225 in interest.

Property taxes. The US national median effective property tax rate is approximately 1.1% of assessed value per year, but the range is extreme: Hawaii is around 0.3%, New Jersey and Illinois approach 2.5%, and most of the Northeast and Midwest is 1.5–2%. On a $250,000 home in a 1.2% tax area, you pay $3,000 per year ($250 per month) in property taxes — an amount that is collected by your lender in escrow monthly and remitted annually.

Homeowners insurance. The national average is approximately $1,700 per year ($142/month) for $300,000 in dwelling coverage, but costs vary substantially by location, construction type, and coverage level. Coastal and hurricane-prone areas pay significantly more. Your lender will require proof of insurance and will escrow for it monthly.

PMI. Private mortgage insurance applies when your down payment is less than 20% of the purchase price. PMI typically runs 0.5–1.5% of the loan amount per year. On a $210,000 loan at 0.7%, that is $1,470 per year or $122.50 per month — a meaningful addition that disappears once your loan-to-value ratio reaches 80%.

Together, these components mean that a $1,800 "mortgage payment" might consist of $1,397 in P&I, $250 in property tax, $100 in insurance, and $53 in PMI. The lender's quoted rate and payment only describe the first piece.

Down Payment: How It Shapes Your Budget

The 20% down payment is a common target but not a universal requirement. Conventional loans backed by Fannie Mae and Freddie Mac allow as little as 3% down. FHA loans require 3.5% with a 580+ credit score. VA and USDA loans allow 0% down for eligible buyers. The choice of down payment amount has cascading effects on your affordability calculation.

PMI threshold. The most significant threshold is 20%. Below it, PMI is required on conventional loans; above it, PMI disappears entirely. On a $250,000 home, the difference between 19% and 20% down ($2,500) eliminates roughly $100–$175 per month in PMI permanently (until the loan reaches 80% LTV through payments).

Buying power effect.Because the down payment reduces the loan amount directly, each additional dollar of down payment increases your maximum home price by approximately one dollar at the margin. This is a near-1:1 relationship because down payment is simply a direct input into the loan size, which drives the monthly P&I. If you have $50,000 in down payment instead of $40,000, your maximum home price rises by approximately $10,000 — the $10,000 simply shifts from "money you borrow" to "money you put in."

Liquidity consideration. Larger down payments reduce monthly costs but reduce your post-purchase liquidity. Financial advisors generally recommend keeping 3–6 months of living expenses in cash reserves after closing, plus a buffer for immediate repairs. Stretching to put 20% down while depleting your emergency fund creates a different kind of financial risk — especially in the first year of homeownership when unexpected costs are most likely.

The practical approach: use this calculator with two scenarios — your actual down payment and a hypothetical one $20,000 higher. Compare the difference in maximum home price and monthly PMI. If saving the extra $20K would take 18 months while renting, calculate whether the monthly savings from no PMI and a lower loan pay back the delay before you plan to sell or refinance.

Interest Rates and Home Buying Power

No single input changes your home buying budget more dramatically than the interest rate. The relationship is not intuitive in magnitude: a 2-percentage-point rate increase reduces purchasing power by roughly 20–25% on a 30-year loan at the same monthly payment.

The math: at 5% on a 30-year loan, a $1,400/month P&I payment supports a loan of approximately $261,000. At 7%, the same $1,400/month supports only $210,000 — a reduction of $51,000 in loan principal from a 2-point rate change. The inverse relationship between rates and purchasing power is the defining variable in most buyers' budgets.

Rate shopping. On a $210,000 loan, a 0.25% rate difference (say, 7.0% vs. 6.75%) translates to about $33 per month — $11,880 over a 30-year term. Getting multiple lender quotes takes about an hour and could save over $10,000. Credit inquiries from mortgage rate shopping within a 14–45 day window are treated as a single inquiry by FICO, so multiple applications do not damage your credit score.

Points and buydowns. One discount point costs 1% of the loan amount and typically reduces the rate by 0.25%. On a $210,000 loan, one point ($2,100) saves about $33 per month. The break-even is around 64 months (5.3 years) — if you plan to stay longer, buying the point is mathematically justified. If you plan to sell or refinance within 5 years, the upfront cost likely exceeds the savings.

Rate environment context.US 30-year fixed mortgage rates averaged 3–4% in 2020–2021 and rose to 7–8% in 2023–2024. The buying power difference between those extremes is enormous: a buyer with a $2,000/month P&I budget could afford a $470,000 loan at 3% but only a $300,000 loan at 7% — a 36% reduction in purchasing power from rates alone. Use this calculator to see how different rate assumptions change your budget in real time.

Existing Debt: How It Constrains Your Budget

The back-end DTI ratio makes your existing debt directly competitive with your housing budget. Every dollar of monthly debt payment reduces your maximum housing payment by exactly one dollar. At current interest rates, that translates to roughly $125–$150 less in maximum loan principal per dollar of monthly debt.

A concrete example: if you have a car loan with a $400/month payment and a student loan with a $200/month minimum, your $600 in monthly debt obligations reduces your maximum housing payment by $600 (under the back-end rule). At 7% on a 30-year loan, $600/month in loan capacity corresponds to approximately $90,000 in loan principal. That $600 in monthly debt costs you approximately $90,000 in home buying power.

Minimum payments vs. balances. The DTI calculation uses minimum required payments, not outstanding balances. A $15,000 car loan might require a $300/month minimum while a $2,000 credit card balance might require a $50 minimum. The credit card balance has less impact on buying power than the car loan, despite being a much smaller balance.

Strategy: pay off before buying. If you have installment debt you could eliminate before applying for a mortgage, calculate whether the resulting increase in buying power justifies the delay. Paying off a $400/month car payment adds roughly $50,000–$60,000 to your buying power. If the car is paid off in 12 months, delaying your home purchase by one year to eliminate it might be worth $60,000 in additional home value — far more than a year's rent in most markets.

You can test this in the calculator: set monthly debts to $0 and see how your maximum home price changes. The difference represents your debt's current cost in buying power.

Pre-Approval vs. Calculated Affordability

Lender pre-approval tells you the maximum amount a lender is willing to lend. This calculator tells you the maximum amount the 28/36 rule suggests you should borrow. These two numbers are often different — and not always by a small margin.

Modern lenders, particularly for buyers with high credit scores (720+) and substantial assets, frequently approve borrowers at 43–50% back-end DTI ratios. A buyer earning $80,000 with a 780 credit score and $30,000 in reserves might receive pre-approval for a mortgage at $1,900/month PITI — 34% of gross income — while this calculator shows a conservative target of $1,867. In that case, the pre-approval and the 28/36 rule align closely. But at 50% back-end DTI, the same buyer might be approved for $2,533/month in housing costs, which would leave far less room for the expenses this calculation ignores.

What pre-approval doesn't include.Pre-approval underwriting does not account for your actual living expenses, childcare, healthcare, retirement contributions, or the ongoing cost of homeownership beyond PITI. Home maintenance typically runs 1–2% of the home's value per year — on a $250,000 home, that is $2,500–$5,000 annually ($208–$417/month) that does not appear in any mortgage calculation but is very real. Closing costs of 2–5% of the purchase price ($5,000–$12,500 on a $250,000 home) require liquid cash on top of the down payment.

The practical guidance: use the pre-approval amount as a ceiling and use this calculator's output as a conservative target. Shopping at 85–90% of your maximum calculated budget provides financial breathing room that the 28/36 rule alone doesn't explicitly reserve.

Using These Results in Your Home Search

The maximum home price from this calculator is a budget ceiling, not a shopping target. Buying 10–15% below your maximum creates meaningful financial margin. On a $250,000 maximum, focusing your search on homes priced $210,000–$230,000 means your housing payment is 10–15% below your budget threshold — enough to absorb unexpected costs without financial stress.

Once you identify a specific listing that interests you, use the companion Mortgage Calculatorto run the exact PITI payment for that home's price, your actual down payment, and current rates. This calculator gives you the budget range; the mortgage calculator checks specific homes within that range.

Before you start, it also helps to know your target down payment timeline. If you're saving toward a down payment, the Savings Goal Calculator will tell you exactly how many months it takes to reach a target down payment at your current savings rate — or the monthly savings amount required to hit a specific down payment by a target date.

If your back-end DTI is the binding constraint — meaning existing debts are limiting your budget more than income alone would — the Debt Payoff Calculator can show you the optimal sequence for eliminating those debts before applying for a mortgage, and exactly how much buying power each payoff restores.

Frequently Asked Questions