Introduction
Lenders will often approve more than you should borrow. Affordability is the loan size you can actually sustain across job changes, rate increases, and life events — not the bank's ceiling.
Definition
Loan affordability is the maximum loan amount where monthly payments stay within a safe percentage of your income, after other debts and essential expenses.
Why It Matters
- Overborrowing is the single biggest driver of foreclosure
- A safer payment leaves room for retirement saving and emergencies
- Affordability rules help avoid being "house poor"
How Lenders Measure It
Most lenders use two ratios:
| Ratio | Formula | Typical Limit |
|---|---|---|
| Front-end DTI | Housing payment ÷ Gross monthly income | ≤ 28% |
| Back-end DTI | All debt payments ÷ Gross monthly income | ≤ 36–43% |
The Consumer Financial Protection Bureau (CFPB) uses a 43% back-end DTI as the threshold for a "qualified mortgage."
The 28/36 Rule
A long-standing guideline:
- Spend ≤ 28% of gross income on housing
- Spend ≤ 36% on total debt (housing + car + student loans + credit cards)
Worked Example
- Gross monthly income: $8,000
- Existing debts: $600/month (car + student loans)
Front-end cap: 0.28 × $8,000 = $2,240/month for housing Back-end cap: 0.36 × $8,000 = $2,880 → minus $600 debts = $2,280/month for housing
Use the smaller — $2,240/month — as the affordable housing budget.
At 7% over 30 years, that supports a loan of about $337,000 (PITI eats some of the $2,240, so the actual P&I might be ~$1,800 → loan ≈ $270,000).
Beyond the Ratios
Affordability ratios ignore:
- Childcare
- Retirement savings
- Medical costs
- Cost of living in your city
- Job stability
A truly safe payment leaves at least 20% of take-home pay for savings and surprises.
Benefits
- Lower foreclosure risk
- Faster path to financial independence
- More resilience to job loss or rate hikes
Common Mistakes
- Maxing out the lender's approval letter
- Forgetting taxes, insurance, HOA, and maintenance (~1% of home value/year)
- Treating bonus or overtime income as guaranteed
- Skipping the emergency fund to stretch into a bigger home
Conclusion
Affordability is a personal calculation, not a credit decision. Use the Loan Affordability Calculator below to find your safe number based on income, debts, and rate.