Methodology and data sources
Appeal Prepper 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 is a distinct current-year screen. It combines precomputed, time-bounded public comparison evidence with a provisional assessment estimate carried forward from the 2025 closed roll. Both the estimate and the property-fact vintage are labeled in the report. The current-assessment estimation method is intentionally provisional while we refine it.
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.
- Rank and weight peers. The model considers timing relative to January 1, distance and neighborhood, living area, bedrooms and bathrooms, year built, lot area for houses, and event quality. The 2026 current-year model also considers zoning compatibility. Distance is its largest single-family match component. Zoning is a soft signal: a mismatch is flagged and downweighted, never automatically excluded. Price is not used to calculate the underlying property-match score.
- Form a conservative range only when support passes the gates. Time- and size-adjusted peer values form weighted 20th, 50th, and 80th percentile estimates. The upper estimate is used to screen the possible assessment gap.
How this relates to the published assessment process
Appeal Prepper 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 Appeal Prepper's documented screening choices. The product does not claim to reproduce an unpublished City valuation model or a licensed appraisal.
Current 2026 property-match weights
Distance 30 · sale timing 28 · living area 11 · lot area 7 · bedrooms 5 · bathrooms 5 · zoning 5 · year built 4 · event quality 3 · named location tier 2.
Sale timing 28 · living area 20 · building or neighborhood tier 16 · distance 10 · bedrooms 8 · bathrooms 8 · zoning 5 · event quality 5.
The point score ranks observable property similarity. The separate range calculation uses multiplicative weights for recency, size, beds and baths, zoning, event quality, location, and distance. This gives especially close homes more influence without allowing one field to erase every other difference.
Range and savings math
Weighted comparison-derived 20th, 50th, and 80th percentile values, adjusted for timing and size.
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 displayed estimate is not a guaranteed reduction. The City, not Appeal Prepper, determines taxable value.
Why some results do not show a range
- Supported screen
- The property and peer set pass the ordinary-home evidence gates, so the pilot may show 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 is not a probability that the assessment is wrong and not 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.