The number on the listing is a lie — by omission
Every major real estate portal shows a mortgage estimate. It's the first number you see, it anchors your thinking, and it's almost always wrong. Not because the math is off — the amortization is fine — but because it represents maybe 60% of what you'll actually pay every month.
Here's what's being omitted, and how to calculate each piece yourself.
Line 1: Mortgage P&I — the only number they show
This is accurate. Standard amortization: M = P × [r(1+r)^n] / [(1+r)^n − 1] where P is principal, r is monthly rate, n is term in months. On a $550,000 purchase with 20% down at 6.875% for 30 years: ~$2,890/mo. This is what listing sites show.
Line 2: Property tax — reassessed (the hidden landmine)
The tax figure on a listing is the seller's tax bill — often artificially low due to years of cap protection. In Florida, the "Save Our Homes" cap freezes assessed value growth at 3%/year for homesteaded properties. A seller who bought 20 years ago might pay $3,900/yr on a home now worth $650,000. You, the buyer, reset to full market value at closing.
Actual buyer tax on a $650,000 Miami-Dade home: ~$11,200/yr ($933/mo). The seller pays $325/mo. That gap — $608/mo — is never shown on any listing site.
Line 3: Homeowners insurance — crisis-level premiums in FL, CA, TX
The national median homeowners insurance premium is around $1,400/yr. In Florida, the average is now $4,200–6,000/yr and climbing — insurers have left the market in droves after hurricane losses. A $650k Miami-Dade home currently costs $450–600/mo to insure. No listing site models this. They either omit it or use a generic national median that's 3× too low for FL.
Line 4: Maintenance reserve — the 1% rule is wrong
The lazy industry shorthand is "budget 1% of home value per year for maintenance." On a $650k home, that's $6,500/yr ($541/mo). The problem: this treats a 2-year-old roof and a 23-year-old roof the same. The right approach is component-based:
- Roof (25yr life, $18k replacement): if 20 years old → $300/mo reserve
- HVAC (15yr life, $8,500): if 12 years old → $189/mo
- Water heater (12yr, $1,800): if 10 years old → $50/mo
Ask for the last permit dates on major systems. This data is public — it's just never aggregated for buyers.
Line 5: Utilities
Electric, gas, water/sewer for a 2,200 sqft home in a hot climate: $250–380/mo. Older homes are leakier; pre-1990 construction in Florida can run $100–150/mo more than a 2010-built equivalent. Request prior-owner utility bills — sellers are generally willing to share, especially in negotiations.
Line 6: HOA and special assessments
HOA fees are usually disclosed. What isn't disclosed: special assessment risk. Post-Surfside, Florida condos are required to fund structural reserve studies — many buildings that had inadequate reserves are now levying $20,000–80,000 per-unit special assessments. If you're buying a condo built before 2000 in Florida, ask for the reserve study before making an offer.
The honest all-in number
Same $650,000 Miami-Dade home, with everything included:
- Mortgage P&I: $2,890/mo
- Property tax (reassessed): $933/mo
- Insurance: $500/mo
- Maintenance reserve: $320/mo
- Utilities: $300/mo
- HOA: $0 (single family)
- Total: $4,943/mo
The listing shows $2,890/mo. You'll actually pay $4,943/mo — 71% more. This is not unusual. Use SeeRew's True Cost calculator to run these numbers on any property before you make an offer.
