Home Affordability Calculator — Max Price & DTI
Find the maximum home price you can afford based on income, debts, and down payment using the 28/36 DTI rule and FHA 43% maximum. Includes PMI estimate and PITI breakdown.
Quick Scenarios
Car, student, credit card minimums
What Is the Home Affordability Calculator — Max Price & DTI?
Lenders use debt-to-income ratios to determine the maximum mortgage they will approve. The front-end ratio limits housing costs alone; the back-end ratio limits all monthly debt payments combined. The lower of the two resulting home prices is the actual constraint.
- ›28% front-end — If your gross income is $8,000/month, maximum monthly PITI is $2,240. This is the threshold most conventional lenders prefer.
- ›36% back-end — If you have $500/month in car and student loan payments, maximum housing is $2,380 ($8,000 × 36% − $500). Back-end is often the binding constraint for buyers with existing debt.
- ›PMI — Private Mortgage Insurance is required when your down payment is below 20%. It adds 0.5–1.5% of the loan amount annually until your LTV reaches 80%. The calculator estimates PMI at 0.5%.
Formula
28% Front-End Rule (Housing)
Max Housing Payment = Gross Monthly Income × 28%
36% Back-End Rule (All Debt)
Max Housing Payment = Gross Monthly Income × 36% − Monthly Debts
43% Maximum DTI (FHA / Conventional limit)
Max Housing Payment = Gross Monthly Income × 43% − Monthly Debts
PITI (Full Monthly Payment)
PITI = Principal + Interest + Property Tax/12 + Insurance/12 + HOA + PMI
| Ratio | What It Limits | Standard Threshold |
|---|---|---|
| Front-End DTI | Housing costs only (PITI) | 28% — Conventional guideline |
| Back-End DTI | All monthly debt payments | 36% — Conservative; 43% FHA max; 50% absolute limit |
| PMI | Required when LTV > 80% | Typically 0.5%–1.5% of loan amount annually |
How to Use
- 1Enter annual income: Use gross (before-tax) household income. Include all reliable income sources.
- 2Enter monthly debts: Include minimum payments on car loans, student loans, credit cards, and other recurring debt. Do not include utilities, groceries, or future mortgage.
- 3Enter down payment: The total dollar amount available for down payment. Less than 20% will trigger PMI in the estimate.
- 4Set interest rate: Use a realistic rate for your credit profile. Check Freddie Mac's PMMS or your lender pre-qualification for a current rate.
- 5Enter property costs: Property tax rate varies widely by state (0.3% in Hawaii to 2.5%+ in NJ). Insurance is typically 0.3–0.8% of home value annually.
- 6Review the results: The recommended price is the lower of what the 28% and 36% rules allow. Review the scenario table to see how different price points affect your DTI.
Example Calculation
$100,000 income, $500/mo debts, $40,000 down, 7% rate, 30-yr
Monthly gross income: $8,333
28% front-end limit: $2,333/mo PITI
36% back-end limit: $8,333 × 36% − $500 = $2,500/mo PITI
Binding constraint: Front-end ($2,333)
Working back from $2,333 PITI:
Property tax (1.1%/12): ≈ $290/mo on $316k home
Insurance: $130/mo
Available for P&I: $1,913/mo
Max loan at 7%, 30-yr: $288,000
Max home price: ≈ $328,000 (loan + $40k down)
Impact of existing debt
With no existing monthly debt ($0 instead of $500), the 36% back-end rule would allow $3,000/mo PITI, permitting a home price of roughly $400,000. Every $100/month in existing debt payments reduces your maximum home price by approximately $15,000–$18,000 at current rates.
Understanding Home Affordability — Max Price & DTI
Why DTI Rules Exist
Debt-to-income ratios are the primary underwriting criteria lenders use to assess default risk. Research from Fannie Mae and Freddie Mac shows that borrowers with back-end DTIs above 43% have significantly higher default rates, particularly during economic downturns. The 28/36 rule dates to the 1970s as a rule of thumb for sustainable housing costs.
Qualifying vs Comfortable Affordability
Just because a lender will approve a mortgage does not mean you should take it. Lenders apply the 43% DTI maximum; financial planners often recommend keeping housing at 25–28% of gross income to leave room for retirement savings, emergencies, and discretionary spending. Buying at the maximum approved price leaves almost no financial margin.
- ›At 28% front-end: typical for first-time buyers in moderate-cost markets.
- ›At 36% back-end: common and manageable for most budgets.
- ›43%+ DTI: technically qualifiable but financially stressful — limited room for saving or unexpected expenses.
PMI: When It Applies and How to Eliminate It
PMI is required when your loan-to-value (LTV) ratio exceeds 80% (down payment below 20%). On a $400,000 home with 10% down, PMI might cost $150–$250/month. Once your loan balance falls to 80% of the original appraised value, you can request PMI cancellation. It terminates automatically at 78% LTV under the Homeowners Protection Act. Alternatives: 80/10/10 piggyback loans, lender-paid PMI (higher rate), or VA/USDA loans for eligible borrowers.
Legal Disclaimer
This calculator provides estimates based on standard underwriting guidelines. Actual loan approval depends on your credit score, complete credit history, asset verification, employment history, and individual lender overlays that may be more or less restrictive than general guidelines. Consult a licensed mortgage professional for personalized pre-qualification or pre-approval. CFPB affordability guidance.
Frequently Asked Questions
What is DTI and why does it matter for a mortgage?
Debt-to-Income ratio is total monthly debt payments ÷ gross monthly income. Lenders use it as the primary measure of your ability to take on additional debt.
- ›Under 36% back-end DTI: strong — most conventional lenders are comfortable here.
- ›36–43% DTI: acceptable but higher scrutiny; may require stronger credit or reserves.
- ›43% DTI: maximum for most conventional loans (Fannie Mae / Freddie Mac guidelines).
- ›Above 43%: most lenders decline; FHA loans can go to 43–50% with compensating factors.
Two ratios are calculated: front-end (housing only) capped at 28%, and back-end (all debt) capped at 36%. The binding constraint determines your maximum home price.
Does this calculator tell me how much I'll be approved for?
It estimates the maximum based on standard DTI guidelines — not a pre-approval. Actual approval depends on several additional factors lenders evaluate.
- ›Credit score: a 620 score may qualify for less; a 780 score with reserves may qualify for more.
- ›Credit history: derogatory marks, collections, or recent late payments reduce approval odds.
- ›Employment history: most lenders want 2+ years of stable income history.
- ›Assets: large reserves signal risk tolerance and may allow higher DTI with some lenders.
Use this calculator for planning and scenario comparison, then get a formal pre-approval from a lender before making offers.
What income should I use — individual or household?
Use whichever income matches who will be on the loan.
- ›Both borrowers on loan: use combined gross household income — all reliable income sources.
- ›Solo borrower: use only your income, even if your partner earns more.
- ›Adding a co-borrower adds their income AND their debts to the back-end DTI calculation.
- ›Part-time / self-employment income: lenders typically require 2-year history and average it.
Adding a co-borrower is worth it when their income boost outweighs the debt they bring to the DTI calculation.
Should I include credit card balances in monthly debts?
Yes — but use the minimum required payment, not the full balance or what you actually pay.
- ›$5,000 balance with $100 minimum: enter $100 in monthly debts.
- ›Cards paid in full monthly: many lenders still count the minimum payment in DTI.
- ›Cards with $0 minimum (no balance): typically not counted in DTI.
- ›Student loans in deferment: most lenders count 0.5–1% of the balance as a monthly payment.
To improve DTI before buying, paying off installment loans (car, student) is often more effective than paying down credit card balances, since installment loans have higher required minimum payments.
How does a higher down payment help?
A larger down payment improves your mortgage in several compounding ways:
- ›Lower loan amount → lower monthly P&I payment → better DTI ratio → higher maximum home price.
- ›Eliminates PMI once you reach 20% down (saves $100–$250/mo on a $400k home).
- ›Lower LTV ratio may qualify you for a better interest rate (0.125–0.25% lower at 20% vs 10% down).
- ›Larger equity buffer protects against short-term price declines.
The main cost of a larger down payment is opportunity cost — the investment return you forgo on those dollars. Weigh the mortgage savings against the expected market return on the capital.