Nearly every successful Philadelphia assessment appeal rests on one thing: proof that homes genuinely like yours sold for less than the Office of Property Assessment says yours is worth. Those homes are your comparable sales, and choosing them well is most of the battle.
A comparable sale — a "comp" — is a recent, open-market sale of a property so similar to yours that its price is fair evidence of what yours is worth. The word doing the heavy lifting is similar. Philadelphia assessments are produced by mass appraisal: the Office of Property Assessment (OPA) runs a standardized model across hundreds of thousands of parcels at once. That model is good at averages and blind to the specifics of your block, so the way to challenge it is to show the specific sales it overlooked.
Six attributes decide whether a sale is truly comparable:
A comp isn't the house closest to yours on a map. It's the house closest to yours in what a buyer would actually pay for it.
Every deed transfer in the city is recorded and flows into the public property data the OPA maintains. You can look up recent sales through the city's property search tools at the phila.gov property portal and cross-check details against the OPA record for each address. The raw data is public, but it is not curated for appeals — you get every sale, including the ones you should throw out, and no flags telling you which are arm's-length. Sorting the signal from the noise is the manual work most of this guide is about. For a broader primer, our knowledge base article on understanding comparable sales walks through the concepts more slowly.
Before you judge any sale, write down your property's attributes exactly as the OPA record lists them: square footage, year built, construction type, stories, units, and lot size. Every comp is measured against this profile. This step doubles as an error check — if the OPA has your square footage or unit count wrong, that alone can be grounds for an adjustment, which we cover in the evidence guide.
Look for homes that actually closed within roughly the past year, as close to you as possible, in ordinary transactions. Discard sheriff sales, estate liquidations, and family transfers — they sell below market and will drag your evidence down or invite the reviewer to dismiss your set.
Keep only sales that match your home on size, age, type, and condition. This is where discipline pays off. A gut-renovated flip two doors down is not a fair comp for an unrenovated home; a 2,400-square-foot corner property is not a fair comp for your 1,100-square-foot interior rowhouse. Cut anything that a reviewer could reasonably call a mismatch.
No two homes are identical, so note where each surviving comp differs from yours and reason about direction. If a comp is larger or more updated than your home, its price should sit above your value; if it is smaller or in worse shape, below. You do not need appraiser-grade math — a clear, honest note ("this sale was 15% larger and recently renovated, so it supports a value well under its price for my home") is persuasive.
Present your strongest handful with address, sale date, sale price, size, and a one-line note on relevance for each. A tight set that a reviewer can absorb in thirty seconds beats a sprawling spreadsheet that buries your best evidence.
The manual version of this method can eat a weekend. TaxAssessmentIQ pulls your live OPA record, then searches recent Philadelphia sales and automatically filters them to the ones genuinely comparable to your home — matching on size, age, type, and proximity, and setting aside the distressed and non-arm's-length deals that would weaken your case. It shows you each selected comp with the reasoning, tells you whether the resulting gap is worth appealing, and drops the set straight into a Board-ready packet. No tool can guarantee an appeal will win, but starting from clean comps is how you give yourself the best shot. If you want to sanity-check the gap yourself first, see whether your home is over-assessed.
Three to five strong comparables usually carry an appeal further than a dozen weak ones. Reviewers weigh how similar each sale is to your home, not how many you can list.
Aim for sales within roughly the past year, ideally close to the assessment date. Older sales can still help in a slow-moving market, but recent ones reflect current conditions and are harder to dispute.
It is risky. A gut-renovated flip sells for far more than a comparable unrenovated home, so using it can make your own value look low. If you must include one, note the renovation and adjust for it explicitly.
Sales are recorded in public records and reflected in the city's property data. You can look them up through the OPA property search, though pulling and filtering them by hand takes time.
Widen your search gradually to a nearby block or a slightly longer time window, keeping the homes as similar as possible. When true comparables are scarce, documented condition problems or record errors can carry more of the argument.
TaxAssessmentIQ gives you a free, honest verdict from the City's own recorded sales — just enter your address, no sign-up and no account. If your home looks over-assessed, you can get a ready-to-file appeal packet for a flat, one-time price, backed by a money-back guarantee. If it isn't worth filing, we tell you that too — for free, before you pay anything.