Methodology and data sources
SF Property Tax Appeal is a preliminary screening tool. It organizes public assessor evidence so a homeowner can decide whether further research is justified; it is not an appraisal or a prediction of an appeal outcome.
What this pilot covers
The current lookup covers ordinary San Francisco condominiums and standard single-family dwellings represented in the 2025 closed assessment roll. Condos and houses are modeled separately. TICs, duplexes, multifamily, mixed-use, restricted-resale, and other special property classes are outside this pilot.
Historical evidence boundary: the result screens the 2025 closed roll using source rolls through 2025 and eligible comparison evidence through March 31, 2025. Current 2026 filing dates are shown as process guidance, but the screen is not a fresh 2026 appraisal.
The 2026 preview combines time-bounded public comparison evidence with an approximate assessment. The existing formula carries the 2025 closed-roll assessment forward unchanged, then rounds it to the nearest $100,000 before it enters a result, export, or ranking. It is not an observed 2026 assessment.
The eventual assessment may differ because of the annual inflation adjustment, ownership changes, new construction, Prop 8 restoration or decline-in-value changes, exemptions, or corrections. The report preserves the 2025 source-roll provenance and estimate method.
How a supported range is produced
- Resolve the assessor record. The lookup matches the entered address to a static copy of public San Francisco assessor data and reads the assessment, property class, living area, lot area when relevant, bedrooms, bathrooms, year built, zoning, and recorded transfer date.
- Keep property segments separate. A condominium is compared with condominium evidence; a single-family home is compared with single-family evidence.
- Prefer recorded consideration. The model uses San Francisco's RTC §408.1 transfer list when it contains a positive parcel-specific price. Multi-APN documents, conflicting prices, self-transfers, implausible values, and unsupported parcel types are excluded. Recorded consideration still does not prove an arm's-length sale.
- Retain older proxies as a labeled fallback. When the two-year transfer list does not cover an older event, a qualifying post-transfer assessment may provide a weaker market signal. These values remain labeled as proxies and are not presented as sale prices.
- Establish eligibility before looking at price. Neutral selection expands a segment-specific location hierarchy only as needed, using timing, observable property facts, and source quality without using sale price or the subject assessment.
- Calculate auditable implied values. Each selected sale price is divided by comparable square feet and multiplied by subject square feet. Only bounded, documented adjustments are allowed; sale price, PPSF, location weight, adjustments, and implied value remain visible.
- Require three report-grade comparisons. Condos and houses use the same gate: every retained comparison is within 1.5 miles; at least two are within 0.75 mile; at least two share the assessor or analysis neighborhood; and at least two are within 270 days of January 1. All evidence remains subject to the applicable March 31 cutoff.
- Allow concentrated evidence. Comparisons do not need to be statistically independent. Three sales in one building may qualify, and one comparison may carry most of the model weight. The report shows the individual matches and weights so the homeowner can judge that concentration directly.
How this relates to the published assessment process
SF Property Tax Appeal uses an independent, transparent comparison model aligned with the categories in San Francisco's Residential Comparison Worksheet and California's published appraisal framework. It is not the Assessor's formula, and the City does not publish a fixed percentage weighting for each field.
For single-family homes, straight-line distance is the largest match component and is also used in the valuation weight. Named neighborhood remains a separate, smaller signal.
In the 2026 current-year report, exact zoning receives full compatibility credit. Different density or use classifications receive a soft penalty and a visible warning because legally permitted use can affect value.
The State handbooks favor comparable properties requiring fewer and smaller adjustments. Our scores rank observable similarity; they do not claim a universal dollar adjustment for a bedroom, square foot, or zoning change.
Condition, views, remodeling, parking, restrictions, and transaction circumstances can outweigh a numerical match. The comparison table is designed to make those review decisions explicit.
Credibility boundary: the categories are grounded in published City and State guidance; the weights are SF Property Tax Appeal's documented screening choices. The product does not claim to reproduce an unpublished City valuation model or a licensed appraisal.
Location strength receives a transparent bounded endpoint weight, with only tightly bounded modifiers. The eligibility policy does not impose an effective-peer-count or maximum-weight constraint.
Range and savings math
A direct implied value from an exceptional match, or favorable and neutral weighted implied-value endpoints from the retained location hierarchy.
Current assessment minus the conservative upper estimate, never less than zero.
Estimated assessment reduction multiplied by the enacted secured-property tax rate for the screened roll.
Estimated gross savings minus the separate $120 City formal-appeal filing fee.
The 2025 roll uses San Francisco's enacted 2025–26 secured-property tax rate of 1.18268325%. See the SF Treasurer secured-property tax page. The filing fee is not deducted from the displayed gross annual savings unless a net first-year scenario is explicitly labeled.
A supported property receives a green signal when estimated gross annual savings are at least $150. Assessment amount, assessment-gap percentage, support tier, effective peer count, range width, and individual weight concentration do not add hidden sale gates. The estimate is exposed so the homeowner can decide whether the $10 report and separate City filing fee make sense.
A displayed estimate is not a guaranteed reduction. The City, not SF Property Tax Appeal, determines taxable value.
Why some results do not show a range
- Supported screen
- The property has at least three comparisons and passes the common location and timing policy, so the product shows a preliminary range and savings scenario.
- Candidate comparisons only
- Potentially useful properties exist, but the aggregate evidence does not support a model-derived range. Candidate rows are research leads, not confirmed comparable sales.
- Insufficient evidence
- The assessor record was found, but the minimum supported peer set was not. Missing evidence is not evidence that an appeal lacks merit, so no negative verdict or savings estimate is inferred.
What “data support” means
The support score summarizes evidence strength: peer count, effective weighted peer count, range width, event quality, subject-record completeness, location quality, and fallback penalties. It remains visible context and is not a sale gate, a probability that the assessment is wrong, or a probability of winning an appeal.
The individual match score ranks observable similarity without using price. It does not verify that a transfer was an arm's-length sale.
Important evidence limitations
Public assessor data does not reliably capture interior condition, remodeling quality, views, floor or orientation, noise, parking, storage, HOA economics, litigation, unusual seller motivation, or title restrictions. Zoning reflects a public-record classification, but it does not by itself establish highest and best use or the value impact of a permitted use. Recorded consideration is identified when present; arm's-length status still requires verification. Older assessment-derived values remain explicitly marked as proxies.
Before relying on a comparison: verify the sale date and price, confirm it was an open-market transaction, and document material differences from the subject property. Consult the City's Residential Comparison Worksheet for the fields the City asks homeowners to consider.
Primary sources used by the product
- San Francisco Secured Property Tax Rolls — assessments and recorded property facts.
- California Revenue and Taxation Code §408.1 — the authority for San Francisco's transfer list, including APN, transfer and recording dates, recording reference, and consideration where known.
- SF Treasurer secured-property tax information — enacted secured-property tax rate.
- SF Assessor decline-in-value guidance — informal-review process and appeal context.
- SF Residential Comparison Worksheet — comparison fields and homeowner evidence format.
- California Property Tax Rule 4 — requires consideration of physical attributes, location, legally enforceable use restrictions, income, and amenities when applying the comparative-sales approach.
- California Assessor's Handbook 501: Basic Appraisal — State guidance on comparable selection, market-supported adjustments, and reconciling value indications.
- California Assessor's Handbook 502: Advanced Appraisal — advanced guidance on deriving and applying comparison adjustments.
- California BOE Publication 30 — an overview of residential property assessment and the comparable-sales approach for taxpayers.
- DataSF Zoning Map — the City's public zoning-district reference. The current comparison signal uses the zoning field carried in the secured assessment roll rather than performing a separate parcel-to-map overlay.
- Assessment Appeals Board hearing guide — formal hearing process.