Waterfront home — 520 S Mashta Drive · Mashta Island A Replat Of · Key Biscayne
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Open property magazine$18,500,000
520 S Mashta Drive, Key Biscayne, FL 33149
Key Biscayne, FL, 33149
5 bd · 4 ba · 3,085 sqft · 138 ft of water
Listed by Coldwell Banker Realty
520 S Mashta Drive, Key Biscayne, FL 33149138 ft of water frontage
Listed by Coldwell Banker Realty
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Know your costs before you buy
Work through three numbers: your estimated monthly payment, the cash needed at closing, and insurance & flood.
Estimated Monthly Payment
20% down · 6.75% interest · 30-year loan · Jumbo loan
Jumbo loan: put down about $17,667,250 or more to stay conforming. What's different?
- A bigger down payment, often 10–20% or more
- A higher credit score, often 700+
- More cash reserves, often 6–12 months of payments
- Full income documentation, sometimes a second appraisal on large loans
Other options: Conforming first mortgage plus a home equity loan for the rest ("piggyback"); Portfolio or private bank loans; Cash. Each lender sets its own rules.
Principal, interest, taxes and insurance. Property Tax (after sale). Estimated; not a lender quote.
- Principal & interest
- $95,993/mo
- Property tax (after sale) est.
- $19,930/mo
- Homeowners insurance est.
- $1,650/mo
- HOA
- $0/mo
Estimate only, not guaranteed. Verify before you buy or sell.
Cash to close
520 S Mashta Drive, Key Biscayne, FL 33149
Estimated cash to close est.
$3,892,155.66
Down payment plus Florida taxes, title, lender and prepaid costs.
Partial estimate: unknown amounts are excluded. Ask Simon to verify them.
Estimate only. Your lender's Loan Estimate and the title company's closing disclosure are the final numbers. Not financial advice.
Estimate only, not guaranteed. Verify before you buy or sell.
Loan amount (calculated): $14,800,000.00Jumbo loan
Above the 2026 $832,750.00 limit, so the daily jumbo rate is used. Put down about $17,667,250.00 or more to stay conforming.
Current site planning rate. Rate does not change the taxes or fees below. Prepaid interest is not included.
Edit closing costs & prepaids
Assumes both policies cover identical land and dates, with loan coverage within owner coverage—even if the seller pays owner title. Minimum lender premium $25. Turn off if not eligible. Endorsement allowance defaults to one $25 endorsement; actual requirements and premiums vary (Florida 69O-186.005).
Appraisal starts at $650. Waterfront and luxury homes may require a higher fee; confirm with your lender.
Tax uses existing ZIP estimates (after sale); insurance uses existing site estimates. Edit with your quote. If HOA insurance is included, confirm separate unit-owner coverage. Missing HOA costs are excluded—not assumed zero.
Estimated cash to close est.
$3,892,155.66
- Down payment est.
- $3,700,000.00
- Mortgage note documentary stamps est.
- $51,800.00
- Mortgage intangible tax est.
- $29,600.00
- Lender’s title insurance est.
- $25.00
- Lender title endorsements est.
- $25.00
- Lender fees est.
- $1,500.00
- Appraisal est.
- $650.00
- Owner’s title insurance est.
- $43,325.00
- Title search & examination est.
- $125.00
- Municipal lien search est.
- $150.00
- Settlement / closing fee est.
- $450.00
- County recording (deed) est.
- $30.00
- County recording (mortgage) est.
- $120.00
- Inspection, wind mitigation & 4-point est.
- $900.00
- Survey est.
- $500.00
- Property tax escrow (2 months, after sale) est.
- $39,860.33
- Insurance escrow (2 months) est.
- $3,299.33
- First-year insurance premium est.
- $19,796.00
- HOA / condo contribution or transfer est.
- Not provided
Partial estimate: unknown amounts are excluded. Ask Simon to verify them.
Mortgage stamps: $0.35 per $100 or fraction. Intangible tax: 0.2% of loan. Title uses Florida 69O-186.003 base rates. Assumes 2 months of tax/insurance escrow for financed purchases plus first-year insurance; cash purchases have no lender escrow.
Before deposits and credits. Prepaid interest and other contract costs are not included. Discounts and title endorsements must be confirmed by the title company. Title search, municipal lien search, settlement and recording are pass-through title company charges for cash and financed buyers alike; the municipal lien search is priced by each city and can run higher (e.g. Boca Raton $150, Coral Gables $220).
Estimate only. Your lender's Loan Estimate and the title company's closing disclosure are the final numbers. Not financial advice.
Estimate only, not guaranteed. Verify before you buy or sell.
Insurance & flood
- Flood zone (FEMA)
- Zone AEFlood insurance required
- Homeowners insurance est.
- $1,650 / month
Flood insurance is required with a federally backed mortgage (FHA, VA, USDA, or a conventional loan from a federally regulated lender). The monthly insurance estimate above does not include flood insurance — see "Show details" for the flood rules and the official FEMA map.
Source: FEMA National Flood Hazard Layer · Date checked: Oct 25, 2026
Insurance estimates vary widely. Get a real quote before you make an offer.
Estimate only, not guaranteed. Verify before you buy or sell.
Flood zone: AE
High-risk mapped flood area (1% annual chance of flooding).
Source: FEMA National Flood Hazard Layer · Date checked: Oct 25, 2026
- Roof type
- Barrel
- Roof year
- Not provided —
- Impact windows / doors
- Impact Glass (Partial)
- Shutters
- Not provided —
- Window features
- Impact Glass (Partial)
- Year built
- 1961
Homeowners insurance: $1,650 / month est.
- Annual premium est.
- $19,491
- Fees & taxes est.
- $305
- Annual total est.
- $19,796
- Likely range est.
- $16,827–$23,755
- Dwelling coverage est.
- $1,203,150
- Other structures est.
- $24,063
- Personal property est.
- $240,630
- Loss of use est.
- $120,315
- Hurricane deductible (2%) est.
- $24,063
The estimated rebuild cost is above the Citizens Property Insurance coverage cap for this county, so this home would need a private carrier.
Based on the listing: 3,085 sq ft · built 1961 · one story · luxury finish level.
Dwelling coverage uses living area × county rebuilding cost. Selling price and land value are not included. The monthly estimate includes fees and applicable taxes.
Broward inland rates were calibrated against two supplied policies; other county and coastal rates have not yet been calibrated against real quotes.
Assumed where the listing is silent: concrete-block construction · coastal rating band · roof 6–15 years old · gable roof · 2% hurricane deductible · admitted carrier; no surplus-lines tax. A newer roof, a hip roof shape, or a higher deductible can lower the premium; frame construction can raise it.
Educational estimate only, not an insurance quote. Actual premiums depend on the carrier, inspections, discounts, and underwriting. Flood insurance not included. Simon Gedz is a Realtor, not a licensed insurance agent.
Special Flood Hazard Area. With a federally backed mortgage (FHA, VA, USDA, or a conventional loan from a federally regulated lender), flood insurance is required.
The FEMA map is a strong indication, not the final answer: your lender orders its own flood zone determination. Cash buyers are not required to carry flood insurance, but on the water it is strongly recommended.
Florida rule: by 2027, Citizens policyholders must carry flood insurance even outside a flood zone, unless the Citizens policy excludes wind coverage. The FEMA map does not show this.
How flood insurance is priced (FEMA Risk Rating 2.0)
Flood insurance is priced home by home, so two neighbors on the same canal can pay very different amounts. Premiums depend on the home's elevation (first-floor height above the expected flood level), distance to water (ocean, Intracoastal, canal or river), the type of flood risk (storm surge, heavy rain or river overflow), the cost to rebuild, the foundation and construction type, and past flood claims on the property.
Federal flood insurance (NFIP) pays at most $250,000 for the building and $100,000 for contents. A luxury waterfront home needs private flood insurance or an "excess flood" policy on top.
Before an offer: pull the official FEMA flood map (FIRMette), ask the seller for an elevation certificate (it largely decides the price), ask whether the seller's existing NFIP policy can be transferred to you (sometimes at a lower rate), and have an insurance agent check prior flood claims (CLUE report). New NFIP policies usually have a 30-day wait before they take effect — don't leave it until the week of closing.
Insurance estimates vary widely. Get a real quote before you make an offer.
Estimate only, not guaranteed. Verify before you buy or sell.
About This Property
Find similar homesSeize a rare opportunity to create a landmark waterfront estate on one of the largest residential lots in Key Biscayne’s exclusive Mashta Island enclave. Spanning an extraordinary 22,140 square feet, this exceptional property offers 138 feet of pristine water frontage and sweeping open water views, providing an unparalleled setting for a world class residence.Plans by renowned architect, Pablo Corazzini of Vitalini Corazzini Architects, are available to the buyer, offering a thoughtfully conceived vision that takes full advantage of the property’s remarkable scale, premier waterfront setting, and spectacular sunsets. The proposed design creates an extraordinary canvas for sophisticated indoor-outdoor living and entertaining, should the buyer choose to pursue the concept.With its exceptional lot size, expansive water frontage, and coveted Mashta Island address, this is a truly irreplaceable opportunity to create a legacy estate in one of South Florida’s most prestigious waterfront communities.
Why we flagged this one
A transparent review of current MLS facts—not a paid placement.
Price reduced 7%
The seller has come down from $19,900,000 to $18,500,000 — a $1,400,000 reduction since it came on the market.
Price reductions and days on market come from this listing's MLS record. This is an initial market signal, not a formal appraisal or full comparable market analysis.
Property Details
Your costs (est.)
≈ $117,572/mo
520 S Mashta Drive, Key Biscayne, FL 33149 · Key Biscayne
Location
520 S Mashta Drive, Key Biscayne, FL 33149
Dock & Draft Match™
Boat size needs on-site verification
Boat fit not verified. Confirm dock length, depth, bridges and ocean access before buying.
One home, every check
Dock & Draft Match™ brings this home's dock length, low-water depth, every bridge, the ocean run, frontage and yacht size together in one place. Estimate only, not guaranteed. Verify before you buy or sell.
What buyers ask about this home
What are the estimated monthly carrying costs at 520 S Mashta Drive, Key Biscayne, FL 33149?+
Property tax (after sale): $19,930/month est.; homeowners insurance: $1,650/month est.; HOA: $0/month. Fixed ownership costs before a mortgage: $21,580/month est. Principal and interest: $95,993/month; PMI: $0/month. Total for the payment scenario shown: $117,572/month est. Flood insurance is not included. Estimate only, not guaranteed. Verify before you buy or sell.
Will property taxes go up after I buy 520 S Mashta Drive, Key Biscayne, FL 33149?+
Usually yes. In Florida the assessed value resets to market value in the year after a sale, so the seller's current tax bill is rarely what a new owner pays. Budget roughly 1.8–2.0% of the purchase price annually until you file for homestead exemption and the Save Our Homes cap (or the 10% non-homestead cap) starts limiting increases.
Does 520 S Mashta Drive, Key Biscayne, FL 33149 need flood insurance, and what drives the premium?+
Most of Key Biscayne sits in a FEMA flood zone, and lenders require flood coverage in high-risk zones. Premiums are driven by elevation certificate, flood zone, roof age and shape, and whether the home has impact windows or accordion shutters. Ask for the current declarations page, the four-point inspection and wind mitigation report early — they set your real cost of ownership.
What should an inspection focus on for a home like 520 S Mashta Drive, Key Biscayne, FL 33149?+
In coastal South Florida, prioritize roof age and permit history, whether windows and doors are impact-rated, the seawall and dock condition on waterfront lots, drainage and elevation, plumbing type (cast iron and polybutylene are common in homes of this era), and any open or expired permits with the city. These items, not cosmetics, drive both price and insurability.
What extra costs come with the waterfront at 520 S Mashta Drive, Key Biscayne, FL 33149?+
Waterfront ownership adds seawall maintenance and eventual replacement, dock and lift servicing, higher flood and wind premiums, and salt-air upkeep on exterior finishes and equipment. Confirm bridge height and water depth at low tide if you plan to keep a boat.
Is there room to negotiate on 520 S Mashta Drive, Key Biscayne, FL 33149?+
This listing has been on the market 85 days. Leverage comes from days on market, price history, comparable closed sales and the seller's motivation — not from a fixed percentage. I pull the full history and the true comps before we write, so the offer is built on what the property is actually worth today. Call or text (954) 562-1798 for that analysis.
Neighborhood & Commute
Located in Key Biscayne, this property offers the South Florida lifestyle — warm-weather living year-round with easy access to the Atlantic coast, A-rated schools, and major business centers.
Approximate Drive Times
Drive times are estimates based on straight-line distance at typical South Florida traffic speeds. Actual times vary with traffic and routing.
Assigned schools for this address
Ponce de Leon Middle
Middle school
Coral Gables Senior High
High school
Zone boundaries published by Miami-Dade County Public Schools.
Other options for this address
Key Biscayne Presbyterian School
Elementary · Private · Christian · Grades PK–K · Key Biscayne
School assignment is set by the district and can change. Always confirm the zoned school with the district before you buy.
Closed sales in the last 12 months, newest first — single-family homes only. Tap a home for its photos and sale facts.
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Simon Gedz
Realtor® since 1995
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$18,500,000 · MLS A12071221
$18,500,000
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