Home Affordability Calculator Guide — 2026
One of the most searched questions in personal finance is "how much house can I afford?" The answer depends on more than just your salary. Your existing debts, down payment size, interest rate, property taxes and insurance all combine to determine your true maximum home price. This guide walks through the DTI-based method used by most US lenders, how different rate environments affect buying power, the PITI calculation, and the key mistakes buyers make when estimating their budget.
Max total monthly debt = Gross monthly income × DTI%
Max housing payment = Max total debt − Existing monthly debts
In PITI mode: PI budget = Max housing − (Tax/12 + Insurance/12 + HOA + PMI)
Max loan = PI budget × [(1+r)^n − 1] / [r × (1+r)^n] (standard mortgage formula)
Max home price = Max loan + Down payment
What Is DTI and Why Do Lenders Use It?
DTI (Debt-to-Income ratio) is your total monthly debt obligations divided by your gross monthly income, expressed as a percentage. Lenders use it because it captures both your income and your existing financial commitments in one number. Two DTIs are typically evaluated:
- Front-end DTI (housing ratio): housing costs (PI + taxes + insurance + HOA) only, divided by income. Most lenders want this under 28%.
- Back-end DTI (total DTI): all monthly debts including housing, car loans, student loans, credit card minimums. Most conventional loans require under 43–45%. FHA loans allow up to 50% with compensating factors.
This calculator uses the back-end DTI, which is the binding constraint for most buyers. A 36% target is conservative and leaves meaningful buffer. If you are near the lender maximum (43–50%), any unexpected income reduction or rate increase could cause financial stress.
PITI — What Your Real Monthly Payment Includes
PITI stands for Principal, Interest, Taxes and Insurance — the four components of a typical US mortgage payment. In most cases, your lender collects property taxes and homeowner's insurance as part of your monthly payment and holds them in an escrow account, paying the bills on your behalf. HOA fees and PMI are additional recurring costs that should also be included in your affordability calculation.
Loan: $280,000 | Monthly PI: ~$1,815
Property tax (annual $5,600): +$467/month
Homeowner's insurance (annual $1,800): +$150/month
HOA: +$150/month
Total PITI + HOA: ~$2,582/month
At 36% DTI this requires gross monthly income of at least ~$7,170 ($86,000/yr) with no other debts.
How Interest Rate Affects How Much House You Can Afford
The rate sensitivity table is one of the most valuable features of this calculator. A 1% difference in mortgage rate translates to roughly 8–10% difference in the loan amount the same monthly payment can support. In a market where rates have moved from 3% to 7% over two years, buyers have lost nearly 30% of their purchasing power on a fixed monthly budget.
| Rate | Max Loan ($1,800/mo PI, 30yr) | Change from 5% |
|---|---|---|
| 4.5% | ~$355,400 | +$31,000 |
| 5.0% | ~$335,700 | Base |
| 5.5% | ~$317,000 | −$18,700 |
| 6.0% | ~$300,100 | −$35,600 |
| 6.5% | ~$284,700 | −$51,000 |
| 7.0% | ~$270,600 | −$65,100 |
| 7.5% | ~$257,600 | −$78,100 |
| 8.0% | ~$245,500 | −$90,200 |
Co-Borrower Income — How Much It Increases Buying Power
Adding a co-borrower (spouse, partner or family member) who also appears on the mortgage application allows the lender to use both incomes for DTI purposes. This is often the single most effective way to increase buying power. A couple each earning $60,000 ($120,000 combined) can qualify for significantly more than either could alone — not just because of the higher income, but because the same debts represent a lower DTI percentage of the larger combined income.
Single earner $90,000/yr: max housing ~$1,950/month → max home ~$300,000
Add co-borrower $60,000/yr: combined $150,000/yr → max housing ~$3,750/month → max home ~$525,000
Co-borrower adds ~$225,000 to buying power — even more if the co-borrower has few debts.
Down Payment — Dollar Amount vs Percentage
The down payment calculator supports both dollar amount and percentage of home price entry. Key thresholds to know:
- 3–3.5%: Minimum for conventional (3%) and FHA (3.5%) loans. Requires PMI.
- 10%: Reduces PMI cost and can improve rate; still requires PMI on most conventional loans.
- 20%: The key threshold — no PMI required on conventional loans. Saves $100–$300+/month.
- 25–30%: Better rate pricing on some jumbo and investment property loans.
Remember: your down payment also needs to cover closing costs (typically 2–5% of the loan amount in the US), so your total cash needed at closing is significantly more than the down payment alone.
What Counts as Monthly Debts for DTI?
- Car loan and lease payments
- Credit card minimum payments (not the full balance)
- Student loan payments (even income-driven repayment amounts)
- Personal loans and installment plans
- Child support and alimony payments
- Other existing mortgage or HELOC payments
Things that do not count: utilities, phone bills, groceries, subscriptions, insurance premiums (other than the housing-related ones), medical bills (unless in collections). Use minimum required payments — not what you actually pay.
Related Calculators
- Loan Calculator — calculate monthly payment from loan amount and rate.
- APR Calculator — understand the true all-in cost of a mortgage.
- Closing Costs Calculator — estimate cash-to-close beyond the down payment.
- Refinance Break-Even Calculator — when does refinancing make sense?
- Investment Return Calculator — model portfolio growth on your down payment savings.
Frequently Asked Questions
1) How much house can I afford on $90,000 salary?
At $90,000/year ($7,500/month), a 36% DTI gives a maximum total monthly debt of $2,700. With $750 in existing debts, your housing budget is $1,950/month. At 6.75% on a 30-year loan, that PI budget supports roughly a $265,000 loan. Add your down payment — e.g. $60,000 — for a max home price of approximately $325,000. The rate sensitivity table shows how this changes with different rates.
2) What is DTI and what is a safe target?
DTI (Debt-to-Income ratio) is total monthly debt payments ÷ gross monthly income. Lenders use back-end DTI (all debts including housing). Conservative target: 36%. Typical conventional loan max: 43–45%. FHA max: 50% with compensating factors. A lower DTI leaves more buffer for unexpected expenses and makes you a lower-risk borrower (which can improve your rate offer).
3) Should I use PITI or PI-only mode?
Always use PITI mode for the most realistic estimate. In the US, property taxes and homeowner's insurance are collected as part of your monthly payment via escrow. Your true monthly housing cost is PITI + HOA + PMI, not just principal and interest. PI-only mode is only useful if you already know your exact PI budget and want to back-calculate the loan amount.
4) Can I include a co-borrower's income?
Yes — enter co-borrower income in the same frequency as your primary income (annual or monthly). The calculator combines both incomes before applying the DTI. This is one of the most effective ways to increase buying power. Note that co-borrowers' debts should also be included in the monthly debts field, since lenders will count both applicants' obligations.
5) How does the interest rate affect my maximum home price?
Dramatically. A 1% increase in rate reduces the loan your payment can support by roughly 8–10%. The Rate Sensitivity table shows your maximum home price at rates from −2% to +2% around your entered rate. Use it to understand your downside exposure and decide whether to lock a rate now or wait.
6) What is PMI and when do I need it?
PMI (Private Mortgage Insurance) is required in the US when your down payment is below 20% on a conventional loan. It costs roughly 0.3–1.5% of the loan per year, or about $50–$200/month on a $250,000 loan. It can be cancelled when you reach 20% equity via paydown or appreciation. FHA loans have their own mortgage insurance premium (MIP) with different rules.
7) Does this include closing costs?
No — this calculator shows monthly payment affordability and max home price. Closing costs in the US typically add 2–5% of the loan amount in upfront cash (origination fees, appraisal, title insurance, prepaid taxes and insurance). Budget for these separately on top of your down payment — your total cash needed at closing is usually significantly more than the down payment alone.
8) Should I enter gross or net income?
Gross income (before tax). Lenders always use gross income for DTI calculations. W-2 employees use their salary before deductions. Self-employed borrowers typically use a 2-year average of net income from tax returns. Contract or 1099 workers may have income averaged differently by lenders — check with your specific lender for their policy.