Home Affordability Calculator
Calculate your buying power based on income & debts.
The Science of Affordability: Decoding the 28/36 Rule
The question “How much house can I afford?” is often answered with vague rules of thumb like “3 times your salary.” In reality, mortgage lenders use a precise mathematical framework to determine your borrowing power. They are less concerned with how much you earn, and more concerned with how much you keep.
Our **Home Affordability Calculator** uses the same “Reverse Amortization” logic as underwriting software. It starts with your maximum safe monthly payment and works backward to find the home price, accounting for the friction of taxes, insurance, and HOA fees.
The Golden Standard: The 28/36 Rule
Most conventional loans conform to the 28/36 rule. This is the bedrock of mortgage qualification.
- Front-End Ratio (28%): Your housing costs (Principal, Interest, Taxes, Insurance) should not exceed 28% of your gross monthly income.
- Back-End Ratio (36%): Your total debt load (Housing + Credit Cards + Student Loans + Car Notes) should not exceed 36% of your gross monthly income.
Understanding Debt-to-Income (DTI)
Your DTI is the single most important number in the mortgage process—even more important than your credit score in many cases. It measures your ability to absorb a new monthly payment.
The formula lenders use to cap your mortgage payment is:
Example: You earn $10,000/month. You have $500 in student loans and $400 in car payments. The bank allows a max DTI of 43%.
\( (\$10,000 \times 0.43) – \$900 = \$3,400 \)
Your max housing budget is $3,400/month. If your debts were $0, your budget would jump to $4,300/month, significantly increasing your purchasing power.
The Hidden Costs: PITI
Novice buyers often look only at the mortgage principal and interest. However, your monthly check to the bank covers four distinct buckets, collectively known as **PITI**.
The money that actually pays off the loan. In the early years of a 30-year mortgage, this is mostly interest.
Property taxes can range from 0.5% to over 2.5% of the home’s value annually. In high-tax states like Texas or New Jersey, this can equal the mortgage payment itself.
Homeowners insurance protects against fire and theft. If you live in a flood zone, mandatory flood insurance can add hundreds to this cost.
The Interest Rate Impact
Interest rates are the lever that moves the world. A small change in rates has a massive impact on affordability because it changes the “cost of money.”
Consider a buyer with a $3,000 monthly budget. Here is how much house they can buy at different interest rates (assuming 20% down):
| Interest Rate | Buying Power | Total Interest Paid (30 Yrs) |
|---|---|---|
| 3.0% | $710,000 | $360,000 |
| 5.0% | $560,000 | $520,000 |
| 7.0% | $450,000 | $630,000 |
Note: As rates rise, your purchasing power collapses because more of your monthly payment goes toward servicing interest rather than paying down the home price.
Strategies to Afford More Home
If the calculator output is lower than you hoped, there are three mathematical levers you can pull to improve your standing.
1. Pay Down High-Interest Debt
Because of the DTI calculation, every $100 of monthly debt you eliminate increases your mortgage buying power by approximately $15,000 (depending on interest rates). Paying off a $400/month car note is often more effective than saving another $10,000 for a down payment.
2. Increase the Down Payment
Putting 20% down eliminates PMI (Private Mortgage Insurance). PMI is a fee charged to risky borrowers that does nothing for you. Eliminating a $150/month PMI fee frees up that cash flow to go toward a more expensive home.
3. Buy Down the Rate
You can pay “Discount Points” at closing. One point usually costs 1% of the loan amount and lowers your interest rate by 0.25%. If you plan to stay in the home for 10+ years, this upfront cost pays for itself in monthly savings and increased buying power.
Frequently Asked Questions
The 43% DTI ratio is generally the “hard ceiling” for a Qualified Mortgage (QM). While FHA loans can sometimes go up to 50% or 55%, most conventional lenders stop at 43%. If your debts + new house exceed 43% of your gross income, your loan application will likely be denied.
Lenders calculate income conservatively. They typically require a 2-year history of bonuses or commissions to count them. They will average your last two years of variable income. If you just started a commission-based job, they may only count your base salary.
No. First-time buyers can often put down as little as 3% (Conventional) or 3.5% (FHA). However, putting down less than 20% triggers PMI, which increases your monthly payment and lowers your maximum purchase price.