Mortgage Payment vs. What You Can Actually Afford
Two of the most-asked questions on the internet — "what's my mortgage payment" and "how much house can I afford" — have completely different answers. This guide bridges the two calculators and shows where each one ends and the next one begins.
Step 1 — The math
Mortgage Calculator
PITI for a specific home price, rate, and term. Answers "what will my payment be?"
Run a paymentStep 2 — The ceiling
Affordability Calculator
Max home price for your income, debt, and state. Answers "how much house?"
Solve for max priceBoth calculators are free, no signup. Bookmark them — most buyers use them 8–12 times before closing.
The 28/36 rule: where both calculators meet
The 28/36 rule is the single most useful bridge between the mortgage calculator and the affordability calculator. It caps your housing costs at 28% of gross income (front-end) and total debt at 36% of gross income (back-end). Built in the 1980s, it remains the most reliable guardrail for not becoming house-poor — even though modern lenders will stretch you to 43% or 45%.
The rule. Leaves room for maintenance, replacement reserves, and life shocks.
Typical FHA/VA approval. Possible if your maintenance reserves are already funded.
Lender stretch cap. Where buyers become statistics on the wrong side of the maintenance curve.
Deep dive: The 28/36 Rule Explained · How Much House You Can Really Afford
What the mortgage calculator misses
The mortgage calculator solves for PITI — principal, interest, taxes, insurance. That's the number the lender underwrites against. The table below shows the line items it does not include, priced for a $500,000 home at 7% with 20% down, US national averages.
| Line item | PITI (mortgage calc) | True monthly | Delta | Why |
|---|---|---|---|---|
| Principal & interest | $3,326 | $3,326 | — | What the mortgage calculator solves for. |
| Property tax (avg national) | $521 | $521 | — | Already in PITI. Rises ~3–5%/yr in most metros. |
| Homeowners insurance | $167 | $215 | +$48 | PITI uses today's premium. Real-world: +30% in coastal markets 2024–2026. |
| Maintenance reserve | — | $417 | +$417 | 1% rule on $500K home. Maintenance calc misses this entirely. |
| Major system replacement | — | $208 | +$208 | Roof, HVAC, water heater amortized over lifecycle. |
| Utilities (above renting) | — | $120 | +$120 | Heating/cooling more sqft. Mortgage calc shows $0. |
| HOA (if applicable) | — | $0–$650 | varies | Average $300/mo nationally for HOA-bound homes. |
| TOTAL — $500K home / 7% / 20% down | $4,014 | $4,807 | +$793/mo | The gap your pre-approval letter doesn't show you. |
On a $500K home, the gap between PITI and true monthly cost is roughly $793/month. Over 5 years, that's $47,580 — almost exactly the cost of one major system replacement. Run your own numbers with the mortgage calculator and True Cost framework.
The right order: a 3-step bridge
Most buyers use these tools out of order — start with the mortgage calculator, get excited about a payment number, then back into a home price. That's how people end up house-poor. Here's the order that protects you:
- 1
Start with the affordability calculator
It runs 28/36 against your income, debt, down payment, and state defaults. Output: a target home-price band (conservative · moderate · aggressive).
- 2
Sanity-check with the mortgage calculator
Take the conservative number from Step 1, plug in today's rate, and confirm the PITI is comfortably under 28% of your gross monthly income. If it's not, drop the home price.
- 3
Layer the True Cost framework on top
Add maintenance reserves (1–3% of home value/year), replacement reserves, and utility deltas. If the all-in monthly cost still fits, you've actually found a home you can afford — not just a payment your lender will approve.
Related research
Frequently asked
What's the difference between a mortgage payment and what I can really afford?
Your mortgage payment (PITI: principal, interest, taxes, insurance) is what the lender cares about — it's the number on your pre-approval letter. What you can actually afford is PITI plus the costs the lender ignores: maintenance reserves (1–3% of home value/year), replacement reserves for major systems (roof, HVAC, water heater), insurance premium escalation, utility costs above renting, and HOA. On a $500K home, the gap is roughly $700–$900/month. Use the mortgage calculator for PITI, the affordability calculator for the lender-cap number, and the True Cost framework for what you'll actually spend.
Should I use the mortgage calculator or the affordability calculator first?
Start with the affordability calculator — it gives you a target home-price band based on income, debt, and your state's tax + insurance. Then run that number through the mortgage calculator to see exactly what the monthly PITI looks like at current rates. Finally, layer the True Cost framework on top to verify you can absorb maintenance + replacement reserves without breaking your budget. Three tools, three different jobs.
Is the 28/36 rule still useful in 2026?
Yes — arguably more useful than ever. The 28% front-end and 36% back-end DTI caps were built to leave room for everything the lender doesn't underwrite: maintenance, taxes rising, insurance creep, life shocks. With 2026 insurance up 30%+ in coastal metros and property taxes rising in most metros, the 28/36 band is closer to the real ceiling than a lender's 36/45 stretch cap.
Why is my pre-approval higher than what the affordability calculator says?
Pre-approval is built against maximum DTI with no reserve for repairs, maintenance, or system replacement. Lenders care that you can pay them — not that the house stays standing. The affordability calculator reserves 1% of home value per year for maintenance (the floor of the 1–3% rule). That gap explains why buyers who use their full pre-approval are also the buyers we hear from a year later, stretched thin against an aging roof or HVAC.
How do property tax and insurance change the picture by state?
Dramatically. Effective property tax ranges from 0.32% (Hawaii) to 2.49% (New Jersey) — a nearly 8x spread. Average homeowners insurance ranges from $950/yr (Oregon) to $5,380/yr (Florida). On a $500K home, that's a $1,000+/month delta between the cheapest and most expensive states for the exact same mortgage. Both calculators bake in state-specific defaults; the True Cost framework adds maintenance benchmarks that vary by climate zone.
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