Four Numbers Called Your Home's Value, and Which One a Buyer Pays

Ask what a house is worth and you can be given four answers, all of them defensible, none of them the same. The confusion this causes is not a failure of any one of them. It is that they were built to answer different questions, and only one of the four is a number anybody actually pays.

The assessed value

What it is: the town's valuation of your property for taxation, produced by mass appraisal — a statistical model applied to every parcel in the municipality at once, based on a record card describing your house that a person may not have looked at in years.

What it is for: dividing the town's tax levy fairly among its property owners. That is a relative exercise. If every assessment in town were 15% low, the tax bills would be identical, because the rate is calculated afterwards from the levy the town is permitted to raise. This is why an assessment being under market is not the windfall people assume — see how Massachusetts property tax works for the levy-first arithmetic behind it.

What it is not: current. Assessments run on a fiscal year and reflect a valuation date already in the past, so in a moving market they lag by design.

The automated estimate

What it is: a model, run on public records and listing data, producing a number for every address in the country without anybody visiting any of them.

What it can see: beds, baths, recorded square footage, lot size, year built, the last sale price and date, and the pattern of nearby sales. On a subdivision of near-identical colonials built in the same decade, those inputs describe the houses well and the estimates are correspondingly decent.

What it structurally cannot see:

Condition. The single largest value variable in most houses, and the one no public record contains. A gut renovation and deferred maintenance for twenty years look identical from the road and identical in the data.
Layout. Four bedrooms is a data field. Whether the fourth is reached by walking through the third is not, and the second fact is worth more than the first. Why layout moves the price takes that apart.
The particular location. Backing onto conservation land and backing onto a commuter rail cut are the same latitude and longitude to within a rounding error.
Everything unrecorded. A new roof, a rebuilt chimney, a finished basement nobody permitted, a septic system replaced last spring.

The honest way to read an automated estimate is as a starting bracket produced by a model that has never seen the house, and to expect it to be least reliable exactly where it matters most — on unusual houses, on unusual lots, in towns with thin sale volume, and in markets that are moving.

The appraised value

What it is: a licensed appraiser's opinion of market value as of a specific date, supported by an adjustment grid of closed comparable sales. A person walks the house.

What it is for: protecting a lender's collateral. That is the whole purpose, and it explains the appraisal's conservatism and its dependence on closed sales rather than on what is happening this month. The full mechanics, and what to do when it comes in low, are in the appraisal guide.

What it is not: a prediction of what a buyer will pay. It is a defensible estimate of what a typical buyer should have paid, looking backwards at evidence.

The sale price

What it is: what one specific buyer paid one specific seller on one specific day, having seen the house and compared it against everything else available to them.

This is the only one of the four that is a fact rather than an opinion, and it is the only one that becomes money. It is also the only one influenced by things no model and no grid will ever hold — how many other buyers wanted it that weekend, whether the buyer had lost two houses already, whether the kitchen happened to be the one they had been looking for.

Why the four disagree, in a single example

Take a house assessed at $780,000, estimated online at $845,000, appraised at $860,000, and sold for $885,000. Nothing has gone wrong. The assessment reflects a valuation date eighteen months back. The model has no idea the kitchen was redone. The appraisal is anchored in sales that closed before the current spring. The sale price is what the strongest of several buyers paid this month. Four processes, four honest answers, four different dates.

The trouble starts when somebody picks whichever of the four suits their position and treats it as the truth. Sellers quote the highest. Buyers quote the lowest. Both are arguing from a number built to answer a question nobody in the room is asking.

What a seller should actually take from this

Do not price from the assessment. It is the wrong date and the wrong purpose, in both directions. A high assessment is not a floor and a low one is not a ceiling.
Do not price from the automated estimate, and do not dismiss it either. Buyers see it. If yours reads well below where you intend to list, work out which of its inputs is wrong — square footage, bedroom count, a missing bathroom — because in most cases you can correct the underlying record.
Check the assessor's field card for errors regardless. It feeds the tax bill, the automated model and, indirectly, what appraisers and agents assume about your house. The correction is free and it is worth an hour.
Expect the appraisal to be the most conservative of the four in a rising market, and plan for it rather than being surprised by it.

What a buyer should take from it

That the online estimate is not a negotiating position. Walking into an offer conversation with a screenshot is the fastest way to be treated as unserious, because the seller's agent knows what the model cannot see and will simply list it. Build your own number from the closed sales — how to read a comp is the method — and use the estimate only to notice when something is far outside the bracket and worth understanding.

The number that is missing from all four

None of them is what the house is worth to you. That number includes the commute you stop making, the school your children walk to, the fact that this is the only four-bedroom on a cul-de-sac that has come up in two years. It is legitimate, it is often higher than all four, and it is also the number that talks people into overpaying.

The discipline is to know both figures separately: what the market says, and what you would pay. Deciding what to do when they disagree is the subject of arriving at your offer.