How comps actually work: the agent's number, the appraiser's number, and the county's number

Updated August 29, 2026. Written by the JB PARCEL team.

Ask what a house is worth and you can get three honest, different answers on the same day. A listing agent says $412,000. A licensed appraiser says $396,000. The county assessor's card says $358,400. None of them is lying. They are answering three different questions with three different methods, and the fastest way to get burned in real estate is to use one professional's number to answer another professional's question.

What a comp is

A comparable sale, a comp, is a recent arms-length sale of a property similar enough to yours that its price says something about your value. Every valuation method in residential real estate is some version of picking comps and adjusting for the differences. The craft is in three choices: which sales count as similar, how far back and how far away you are willing to look, and how much each difference is worth in dollars.

Arms-length matters more than beginners expect. A sale between family members, a foreclosure auction, a deed moving a house into the owner's own LLC for $10 - these are recorded sales, but they are not market prices. Counties that publish sale qualification codes mark them, and any comp set that does not screen them out will skew low.

The agent's number: the CMA

A comparative market analysis is a pricing tool, not an appraisal. The agent pulls recent nearby sales, active listings, and pending contracts, then positions your property against them to answer a marketing question: what price attracts a buyer in the next 30 to 60 days? Active and pending listings are the tell - an appraiser barely weighs them, but to an agent they are the competition your listing has to beat this weekend.

A CMA is fast, free, and current. It is also produced by someone who may want the listing, and optimism wins listings. Judge a CMA by its comps, not its conclusion: if the three closed sales inside it genuinely resemble the house, the number is usually solid.

The appraiser's number: the appraisal

A licensed appraiser answers a lending question: if the borrower defaults, can the collateral cover the loan? The method is standardized on the sales-comparison grid. Typically three to six closed sales, usually within the last six months and within a mile in a suburb, each adjusted line by line - square footage, condition, garage bays, lot size - toward the subject property. The adjusted values are reconciled into one opinion of market value, signed under license and federal appraisal standards.

Appraisals are conservative by design and they look backward, because closed sales are history. In a fast-rising market the appraisal trails the contract price; in a falling one it can sit above what any buyer will actually pay. It remains the most defensible single number in the business, which is why lenders and courts run on it.

The county's number: the assessment

The assessor is not valuing your house for a sale at all. The county needs a defensible value for every parcel it taxes, refreshed on a cycle that ranges from annually to every five or six years depending on the state. That is mass appraisal: statistical models over thousands of properties, calibrated to sales in bulk, never a walk-through of yours. Between reappraisal years the number often stands still while the market moves, and in most states the taxable "assessed value" is only a statutory fraction of the appraised value, which is why the tax card can read absurdly low next to a Zillow screen.

So never read a county appraisal as market value. Read it as a consistent baseline: it was produced the same way for every parcel in the county, in the same year. That makes it one of the best screening denominators in real estate. A house listed at 2.4 times its county appraisal when the neighborhood trades at 1.5 times is either special or overpriced, and either way it has earned a closer look.

Which number for which decision

Building a comp set you can defend

Recent beats similar, similar beats close, and all three beat a bigger sample of junk. Start with sales from the last six months within the immediate neighborhood, throw out anything that fails the arms-length test, and only widen the net when you have fewer than three survivors. Adjust in dollars, not vibes, and write the adjustments down - if you cannot say what a second bathroom is worth in that market, you are guessing with extra steps. On the JB PARCEL map, any parcel's card shows recent comparable sales nearby with dates and prices from county records, plus the county appraisal for the baseline, which covers the screening pass before you ever call an agent or an appraiser.