640 S Mashta Dr
Key Biscayne, FL 33149 · single_family · For Sale · 153 days on market
Asking price$16,800,000
4 beds 4 baths 3,620 sqft
Suggested offer$4,796,210$12,003,790 above the est. market value of $4,796,210.
View on Realtor.com →Listed by Brigitte De Langeron · DLS International Realty
Typesingle_family
Built1968
Price / sqft$4641
Est. value (own analysis)$4,796,210
Rent estimate (own analysis)$19,000/mo
HOANone
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Statusfor_sale
Listed date2026-04-02
Removed date—
MLSMiamiMLS #A11990382
Coordinates25.68471, -80.17456
Address640 S Mashta Dr
CityKey Biscayne
StateFL
Zip33149
Listing ID6263108645
Sourceus-real-estate-listings, cached 2026-08-31
ZIP market snapshot (33149)
Typical home value (ZHVI)$1,692,135
Typical rent (ZORI)$7,910/mo
Zillow Research's ZHVI (home value index) and ZORI (rent index) for this ZIP, as of 2026-07 — free published data, refreshed monthly, no RentCast quota spent. "Typical value/rent" is a smoothed index, not a literal median of active listings.
Underwriting (buy-and-hold, default assumptions)
| Acquisition (one-time, not monthly/yearly) | |
| Purchase price | $16,800,000 |
| Down payment (20.0%) | $3,360,000 |
| Loan amount | $13,440,000 |
| Closing costs (5.0%) | $840,000 |
| Total cash to close | $4,200,000 |
| Income | |
| Rent (comp-derived) | $19,000$228,000 |
| Vacancy loss (8.0%) | |
| Effective gross income | $17,480$209,760 |
| Operating expenses | |
| Property tax (placeholder 1.9% of price) | $26,600$319,200 |
| Insurance (placeholder 0.8% of price) | $11,200$134,400 |
| HOA dues | $0$0 |
| Management (0.0% of EGI) | $0$0 |
| Maintenance (5.0% of GSR) | $950$11,400 |
| Total operating expenses | $38,750$465,000 |
| Net operating income (NOI) | |
| Debt service & reserves | |
| Debt service (6.66%, avg 30yr rate as of 2026-08-27, 30yr amortizing) | |
| CapEx reserve (5.0% of GSR) | $950$11,400 |
| Mortgage insurance (PMI) (0.0% of loan, not required — down payment ≥ 20%) | $0$0 |
| Cash flow |
Cap rate
Cash-on-cash
DSCR
Rent-to-price (1% rule)
Gross rent multiplier
Operating expense ratio
Break-even occupancy
Comparables
Same ZIP. Real active rental listings, used to derive the rent estimate above.
| Address | Type | Beds | Baths | Sqft | Asking rent | Listed | Days on market |
|---|---|---|---|---|---|---|---|
| single_family | 4 | 3 | 2,749 | $19,000 | 2026-08-25 | — | |
| single_family | 4 | 5 | 3,202 | $31,500 | 2026-07-24 | — | |
| single_family | 4 | 4 | 3,006 | $18,900 | 2026-07-29 | — | |
| single_family | 4 | 3 | 2,406 | $19,000 | 2026-05-29 | — |
Same ZIP & bedroom count. Closed sales from Realtor.com over the last 12 months, matched to this property's type — real transaction prices, not asking prices. Falls back to Miami-Dade County public records (property appraiser tax roll) when Realtor.com has no sales on file for the area.
| Address | Type | Beds | Baths | Living sqft | Sale price | Sale date |
|---|---|---|---|---|---|---|
| 301 Hampton Ln | single_family | 4 | 3 | 2,068 | $3,100,000 | 2026-08-24 |
| 591 N Mashta Dr | single_family | 4 | 5 | 4,290 | $14,000,000 | 2026-08-03 |
| 217 Buttonwood Dr | single_family | 4 | 3 | 2,503 | $3,500,000 | 2026-06-23 |
| 401 Warren Ln | single_family | 4 | 3 | 2,958 | $3,000,000 | 2026-04-20 |
| 465 Hampton Ln | single_family | 4 | 4 | 3,666 | $4,475,000 | 2026-04-10 |
| 760 Glenridge Rd | single_family | 4 | 6 | 4,142 | $625,000 | 2026-04-09 |
| 315 Palmwood Ln | single_family | 4 | 5 | 3,297 | $4,400,000 | 2026-04-08 |
| 285 W Enid Dr | single_family | 4 | 3 | 3,436 | $4,200,000 | 2026-04-02 |
| 340 Ridgewood Rd | single_family | 4 | 3 | 2,699 | $3,550,000 | 2026-03-12 |
| 600 Allendale Rd | single_family | 4 | 4 | 2,775 | $3,500,000 | 2026-01-16 |
| 361 W Heather Dr | single_family | 4 | 3 | 1,570 | $2,600,000 | 2025-09-19 |
| 92 W Mashta Dr | single_family | 4 | 3 | 2,403 | $3,230,000 | 2025-09-12 |
Same ZIP. Other properties currently for sale nearby — asking prices, not closed sale prices. Not a price comp; see Sold comps for actual transaction history.
| Address | Type | Beds | Baths | Sqft | Asking price | Days on market |
|---|---|---|---|---|---|---|
| 200 Ocean Lane Dr Apt 501 | condos | 4 | 4 | 1,880 | $3,850,000 | — |
| 201 Crandon Blvd Apt 174 | townhomes | 4 | 6 | 3,254 | $5,100,000 | — |
| 255 Ridgewood Rd | single_family | 4 | 3 | 2,177 | $3,550,000 | — |
| 100 Cape Florida Dr | single_family | 4 | 9 | 8,240 | $19,800,000 | — |
| 161 Cape Florida Dr | single_family | 4 | 6 | 6,661 | $14,990,000 | — |
| 631 N Mashta Dr | single_family | 4 | 5 | 2,255 | $18,500,000 | — |
| 445 Grand Bay Dr Apt 303 | condos | 4 | 5 | 3,480 | $3,850,000 | — |
| 350 E Ocean Dr Unit 301N | condos | 4 | 7 | 3,798 | $8,950,000 | — |
10-year hold projection
IRR-10.8%
Equity multiple-0.84x
Total return (10yr)-$5,518,388
| Year | Property value | NOI | Cash flow | Loan balance | Equity |
|---|---|---|---|---|---|
| 1 | $17,304,000 | -$255,240 | -$1,303,069 | $13,294,281 | $4,009,719 |
| 2 | $17,823,120 | -$260,572 | -$1,308,686 | $13,138,554 | $4,684,566 |
| 3 | $18,357,814 | -$266,006 | -$1,314,412 | $12,972,134 | $5,385,679 |
| 4 | $18,908,548 | -$271,544 | -$1,320,249 | $12,794,286 | $6,114,262 |
| 5 | $19,475,804 | -$277,186 | -$1,326,198 | $12,604,225 | $6,871,580 |
| 6 | $20,060,079 | -$282,935 | -$1,332,262 | $12,401,112 | $7,658,967 |
| 7 | $20,661,881 | -$288,793 | -$1,338,442 | $12,184,051 | $8,477,830 |
| 8 | $21,281,737 | -$294,761 | -$1,344,740 | $11,952,084 | $9,329,654 |
| 9 | $21,920,189 | -$300,840 | -$1,351,158 | $11,704,188 | $10,216,002 |
| 10 | $22,577,795 | -$307,032 | -$1,357,698 | $11,439,268 | $11,138,527 |
Assumes 3.0% annual rent growth, 2.5% expense growth, 3.0% appreciation, and a 6.0% selling cost at exit — all placeholder assumptions, not market-derived.