The math behind this calculator (click to expand)
The 28/36 ceilings give a maximum monthly housing payment: front_end_max = gross_monthly_income * 0.28 and back_end_max = gross_monthly_income * 0.36 - other_monthly_debts. The lower of the two is the binding constraint.
That maximum housing payment is the sum of P&I, monthly property tax, monthly homeowners insurance, monthly HOA, and PMI (if applicable). The calculator solves for the home price by inverting the standard amortization formula at the entered interest rate and term, then adjusting for the down payment percentage and the property tax / insurance / PMI overhead. PMI applies if the down payment is below 20% on a conventional loan and is estimated at roughly 0.7% of the loan amount per year.
Implementation by Michael.
How the 28/36 Rule Actually Works (With Math)
The 28/36 rule sets two ceilings on your debt-to-income ratio. The front-end ratio (28%) caps your total housing costs - principal, interest, property tax, homeowner's insurance, HOA dues, and PMI - at 28% of your gross monthly income. The back-end ratio (36%) caps all recurring debt obligations (housing plus auto loans, student loans, credit card minimums, and any other installment debt) at 36%.
For someone earning $125,000/year, gross monthly income is $10,417. The 28% front-end limit allows $2,917/month for housing. The 36% back-end limit allows $3,750/month total - so if you carry $450/month in existing debts, your housing budget under the back-end rule is $3,300/month. In this case, the front-end rule is more restrictive ($2,917 vs. $3,300), so it controls. This calculator shows both limits and uses the lower of the two as your conservative maximum.
DTI Thresholds Vary by Loan Type
The 28/36 rule is a guideline, not a universal underwriting standard. Conventional loans backed by Fannie Mae and Freddie Mac will approve borrowers up to 45%-50% back-end DTI if automated underwriting finds compensating factors (strong credit, large reserves, low LTV). FHA loans officially cap at 43% back-end but routinely approve 50% with manual underwriting and compensating factors. VA loans have no hard front-end limit and use 41% as a residual income guideline rather than a strict DTI cap.
This matters because a borrower at $125,000 income with $450 in debts could qualify for a housing payment of $2,917/month under the 28% rule, $4,767/month under a 50% FHA approval, or even more with VA eligibility. The gap between "what you qualify for" and "what you can comfortably afford" is where financial stress lives. This calculator defaults to the conservative 28/36 rule because that's the boundary where default rates stay low.
Costs This Calculator Can't Capture
Your mortgage payment is only the beginning. The 1% rule - budget 1% of your home's value annually for maintenance - means a $387,500 home should reserve $3,875/year ($323/month) for roof repairs, HVAC replacement, plumbing, and the rest. HOA fees in condo or planned communities can add $200-$800/month depending on amenities and location. Utilities for a single-family home typically run $250-$400/month depending on climate zone and square footage. None of these costs appear in DTI calculations, but they all come out of the same paycheck.
A realistic total housing cost for a $387,500 home at 6.75% with 20% down, 1.1% property tax, and $1,200/year insurance is approximately $2,585/month for PITI alone. Add $323 for maintenance reserves, $250 for utilities, and potentially $350 for HOA, and you're at $3,508/month - 33.7% of gross income on a $125,000 salary. The DTI calculation says 24.8%, but the real burden is materially higher.
Interest Rate Impact on Purchasing Power
Rates dominate the affordability equation. At a $125,000 income with $450 in monthly debts and 20% down, this illustrative sensitivity table shows how the 28% rule maximum shifts across assumed rates:
- At 5.00%: Maximum home price of approximately $487,000 - monthly PITI of $2,917
- At 6.00%: Maximum home price of approximately $435,000 - monthly PITI of $2,917
- At 6.75%: Maximum home price of approximately $399,000 - monthly PITI of $2,917
- At 7.50%: Maximum home price of approximately $366,000 - monthly PITI of $2,917
- At 8.00%: Maximum home price of approximately $348,000 - monthly PITI of $2,917
The housing budget stays fixed at $2,917/month (28% of $10,417), but the home price it can support drops by $139,000 between 5% and 8%. Each 1-percentage-point rate increase costs roughly $46,000 in purchasing power at this income level. That's the math behind "marry the house, date the rate" - though refinancing isn't free and isn't guaranteed.
Down Payment Strategy: PMI vs. Opportunity Cost
Putting 20% down on a $387,500 home means parking $77,500 in home equity that earns no return. At 10% down ($38,750), you'd pay PMI - typically 0.5%-1.0% of the $348,750 loan, or roughly $145-$290/month - until reaching 78% LTV through normal amortization (approximately 9 years at 6.75%). The total PMI cost over that period: $15,700-$31,300.
Meanwhile, an invested down-payment difference has an uncertain return, while avoided mortgage interest and PMI are contractual savings. Freddie Mac's PMMS 30-year average was 6.55% on July 16, 2026, but your decision should use the actual Loan Estimate and PMI quote plus conservative investment scenarios.
Regional Purchasing Power: Same Income, Different Reality
A $125,000 household income buys dramatically different homes depending on location (the examples below use an illustrative 20% down payment, 6.75% rate, and 28% front-end rule):
- Atlanta, GA (0.88% property tax, ~$1,100 insurance): Maximum home price around $418,000. Median home price ~$375,000. You're above median with room for competitive neighborhoods.
- Dallas, TX (1.69% property tax, ~$2,400 insurance): Maximum home price around $356,000. Median home price ~$365,000. Right at the median - workable but tight in desirable suburbs.
- San Francisco, CA (0.73% property tax, ~$1,800 insurance): Maximum home price around $432,000. Median home price ~$1,350,000. You'd need $918,000 more to reach median. The math doesn't work without a co-borrower or significant assets.
Property tax rates and insurance premiums shift your affordable price by $30,000-$80,000 in either direction. Always use county-specific rates - state averages can be misleading, especially in states with wide intra-state variation like Texas (1.2%-2.5% depending on county) and New York (0.8% in Manhattan to 2.5%+ on Long Island).
Jumbo Loan Limits and High-Price Affordability
For 2026, the one-unit conforming-loan baseline is $832,750 in most counties. Designated high-cost counties can use higher limits, up to the ordinary national ceiling of $1,249,125. A loan above the applicable county limit is jumbo. Jumbo pricing and underwriting requirements vary by lender; borrowers may encounter higher credit, down-payment, reserve, or documentation requirements.
For a borrower targeting a $1.1 million home, a 20% down payment leaves an $880,000 loan. That is above the 2026 baseline but can remain conforming in a county whose published limit is at least $880,000. The classification depends on the property county, not the state average. Check FHFA's county table before assuming conforming or jumbo pricing, then compare actual lender requirements.
How Credit Score Shifts Your Affordable Price
Credit score can affect the rate, points, mortgage-insurance pricing, and programs offered, but the adjustment is lender- and loan-specific. In an illustrative comparison, a 0.75-percentage-point rate gap can reduce the affordable price by tens of thousands of dollars at a fixed payment budget. Compare actual Loan Estimates rather than treating a credit-score band as a guaranteed rate.
Below 620, conventional options narrow significantly. FHA loans accept scores down to 580 (with 3.5% down) or even 500 (with 10% down), but FHA mortgage insurance premiums - 1.75% upfront plus 0.55%/year for the life of the loan - add meaningful cost. A $350,000 FHA loan carries $6,125 in upfront MIP and $160/month in annual MIP, compared to $0 for a conventional borrower putting 20% down. If your score is below 700, improving it by even 40 points before applying can save more than making a larger down payment.
What might change in the next 24 months
FHFA set the 2026 one-unit baseline at $832,750 and the ordinary high-cost ceiling at $1,249,125. FHFA recalculates limits annually from its House Price Index, but the next year's amount should not be assumed before the agency publishes it. A higher limit can move a borderline loan from jumbo to conforming; the pricing effect depends on lender and borrower terms.
Mortgage rates remain a major affordability lever. Freddie Mac's 30-year PMMS average was 6.55% on July 16, 2026. A lower rate increases the loan a fixed payment can support, but future rates are unknown; test several scenarios instead of relying on a forecast or assuming a refinance.
Property insurance is the underappreciated affordability headwind. Homeowners insurance premiums rose roughly 12% nationally in 2024 and another 8 to 10% in 2025 (per state insurance commissioner reports), with double-digit increases in FL, CA, LA, and CO driven by hurricane, wildfire, and convective-storm exposure. The default $1,200/year insurance assumption is now low for many markets; check your county's actual premium rather than the national median.