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Single Family ResidenceResidential
$2,843,317$1,451 / ft²
TopHap EstimateOur estimate of what this home would sell for today, based on nearby sales, the home's size and features, and local price trends. It is a starting point, not an appraisal.· confidence 91How well the pricing models agreed with each other on this home. Higher means the estimate rests on stronger, more consistent data.· as of Sep 24, 2026
Last sold for $2,300,000 on Sep 20, 2022

421 ALDER LN

SAN MATEO, CA 94403
3
Beds
2
Baths
1,960 ft²
Living AreaTotal finished area of the structures, from county records. Some counties include shared space like hallways or a building gym, so it may not match a listing.
0.15 ac
Lot SizeThe size of the land the home sits on, from county records.
1951
Year BuiltThe year the home was originally built, according to county records.
1
StoriesHow many floors the home has above ground.
7
RoomsThe total room count in county records. Counties differ on which rooms they count, so compare it loosely.
2
ParkingThe number of parking spaces on the property, including the garage.

Valuation

$2.8M
$2.6M low$3.1M high
Last SaleThe most recent sale price and date from the recorded deed. Transfers between family members or companies may not reflect market value.$2,300,000 · Sep 20, 2022

Tax & Assessment

Property TaxThe property tax billed for this tax year. It usually pays for schools, roads, and local services.$28,578 (2025)
Assessed ValueThe value the county assigns to this home to calculate property tax. It is often lower than what the home would sell for.$2,440,777 (2026)
Assessed LandThe share of the county's assessed value that comes from the land itself, not the buildings.$1,841,195
Assessed ImprovementsThe share of the county's assessed value that comes from the buildings and other structures on the land.$599,582
Previous AssessedThe county's assessed value from the year before, useful for seeing how the assessment changed.$2,392,920
Assessor Market ValueThe county assessor's own opinion of market value. It is separate from our estimate and updates on the county's schedule.$1,988,730

Property Facts

Property TypeThe broad category the county puts this property in, such as residential or commercial.Single Family Residence
CountySAN MATEO
Lot (acres)The size of the land the home sits on, from county records.0.15
HeatingThe type of heating system in the home.Central
CoolingThe type of cooling or air conditioning in the home.Central
FireplaceWhether the home has a fireplace, and what kind.Yes
PoolWhether the property has a pool, and what kind, such as in-ground.No

Transaction History(3)

Sales and refinances filed with the county for this home. Not every transfer is a normal sale, so check the type before comparing prices.

Assigned SchoolsThe public schools this address is zoned for. Boundaries change, so confirm with the district before you count on it.

H
Hillsdale High SchoolA-
High · Grades 9–12 · 0.2 mi
M
Abbott Middle SchoolC
Middle · Grades 6–8 · 0.3 mi
E
Laurel Elementary SchoolD
Elementary · Grades KG–5 · 0.3 mi

District: San Mateo-Foster City Elementary School District

Neighborhood · ZIP 94403These are comparison scores, not percentages. 100 equals the national average, so 150 means about 50% above average.

CrimeLocal crime compared with the rest of the country, where 100 is average. It reflects things like population density, income, and how crime gets reported.104
Air pollutionOverall air pollution compared with the rest of the country, where 100 is average. Lower is cleaner.85
EarthquakeEarthquake risk and likely building damage compared with the rest of the country, where 100 is average. Scores can run far above 100.516

Index scale: 100 = US average (tick). Lower is better.

Homes occupiedThe share of homes here that someone lives in. The rest sit empty, including vacation and for-sale homes.96%
Bachelor's or higherThe share of adults 25 and older whose highest degree is a bachelor's degree.34%
Poverty rateThe share of people whose household income falls below the federal poverty line, which varies by family size.7.9%
UnemploymentThe share of men 16 and older who are out of work and actively looking. Only men are counted in this figure.1.3%
PopulationHow many people live in this area.43,216
DensityPeople per square mile. Higher numbers mean a more crowded, urban area.7,529 / mi²
Median incomeThe middle household income here — half of households earn more, half earn less.$160,514
Average incomeThe average household income. It runs higher than the median when a few high earners pull it up.$196,016
Average tempThe average temperature here across a full year.58°F
Annual precipHow much rain and melted snow falls here in a typical year.21 in
SunshineThe share of daylight hours that get direct sun in a typical year, counting cloud cover.66%

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Data by ATTOM. Valuations are automated estimates, not appraisals. Photos from Google Street View and may not depict the current property state.

How this home compares

421 Alder Ln measured against every home in its neighborhood, its ZIP code and its county, using county assessor records refreshed nightly. A home can stand out in one of those areas and look ordinary in another, because each one holds a different mix of homes.

  • Worth more than 97% of homes in Westwood Knolls
  • Costs more per square foot than 93% of homes in San Mateo 94403
  • Bigger than 72% of homes in San Mateo 94403
  • Newer than 76% of homes in Westwood Knolls

What homes are worth in San Mateo 94403

Each bar is how many homes fall in that price range. The marker is this home.

This home
$562K$2.9M

This home is worth more than 97% of homes in San Mateo 94403.

How it measures up in San Mateo 94403

The dot is this home. The mark in the middle is the typical home in San Mateo 94403.

Estimated value$2,843,317
CheaperTypical $1,722,444Pricier

Pricier than 97% of homes nearby

Price per ft²$1451
CheaperTypical $1074Pricier

Pricier than 93% of homes nearby

Living area1,960 ft²
SmallerTypical 1,540 ft²Bigger

Bigger than 72% of homes nearby

Lot size0.15 ac
SmallerTypical 0.14 acBigger

Bigger than 56% of homes nearby

Year built1951
OlderTypical 1955Newer

Newer than 37% of homes nearby

How 421 Alder Ln ranks against every home in each area.
MeasureThis homeWestwood KnollsSan Mateo 94403San Mateo County
Estimated valuepricier than$2,843,31797% of homes97% of homes84% of homes
Price per ft²pricier than$145187% of homes93% of homes86% of homes
Living areabigger than1,960 ft²67% of homes72% of homes66% of homes
Lot sizebigger than0.15 ac63% of homes56% of homes55% of homes
Year builtnewer than195176% of homes37% of homes32% of homes

About 421 Alder Ln

How much is 421 Alder Ln, San Mateo, CA worth?

The TopHap Estimate for 421 Alder Ln, San Mateo, CA is $2,843,317 as of Sep 24, 2026. The likely range is $2,573,455 to $3,113,179. The estimate is modelled from recorded sales, assessments and the property's own characteristics — it is not an appraisal.

When did 421 Alder Ln, San Mateo, CA last sell?

421 Alder Ln, San Mateo, CA last sold on Sep 20, 2022 for $2,300,000, according to the county's recorded deed.

How big is 421 Alder Ln, San Mateo, CA?

421 Alder Ln, San Mateo, CA has 3 bedrooms, 2 bathrooms, 1,960 square feet of living space and a 0.15-acre lot.

When was 421 Alder Ln, San Mateo, CA built?

421 Alder Ln, San Mateo, CA was built in 1951, making it 75 years old. The building has 1 story.

What schools serve 421 Alder Ln, San Mateo, CA?

421 Alder Ln, San Mateo, CA is assigned to Hillsdale High School (high), rated A-; Abbott Middle School (middle), rated C; Laurel Elementary School (elementary), rated D. All sit in San Mateo-Foster City Elementary School District. Attendance boundaries change — confirm with the district before relying on an assignment.

How does 421 Alder Ln, San Mateo, CA compare to other homes in San Mateo 94403?

Among the 11,698 homes in San Mateo 94403, it is worth more than 97% of them ($2,843,317 against a typical $1,722,444), its price per square foot is higher than 93% of them ($1451 against a typical $1074), it is bigger than 72% of them (1,960 ft² against a typical 1,540 ft²), its lot is bigger than 56% of them (0.15 ac against a typical 0.14 ac) and it is newer than 37% of them (1951 against a typical 1955). Measured against all of San Mateo County, it is worth more than 84% of homes there. These shares are recounted nightly from the full county assessor record for each area, not from active listings.

What are the property taxes on 421 Alder Ln, San Mateo, CA?

The 2025 property tax bill for 421 Alder Ln, San Mateo, CA was $28,578. The county assessed it at $2,440,777.

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Assigned schools

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