Comparable sales, often called “comps,” are recent transactions of similar properties used to estimate the market value of another property. When an appraiser, real estate agent, or tax assessor needs to figure out what a home or building is worth, they look at what buyers actually paid for similar properties nearby. This approach is the most common method for valuing residential real estate, and variations of it apply to commercial property and even business acquisitions.
How Comparable Sales Work
The logic is straightforward: if three houses on your street sold in the past few months for between $340,000 and $360,000, and those houses are similar to yours in size, condition, and features, your home is probably worth something in that range. Rather than relying on abstract formulas, comps ground a property’s value in what real buyers were willing to pay in the real market.
Appraisers typically select three to six comparable sales, then adjust each sale price up or down to account for differences between the comp and the property being valued. The adjusted prices create a value range, and the appraiser uses professional judgment to land on a final opinion of value within that range. Lenders require this process before approving a mortgage because it protects them from lending more than a property is actually worth.
What Makes a Property “Comparable”
Not every recent sale qualifies as a useful comp. For a property to be considered comparable, it needs to be similar across several dimensions:
- Location: The closer, the better. Comps from the same neighborhood or subdivision carry the most weight. Properties across a major highway, in a different school district, or in a noticeably different area are less reliable even if they’re only a mile away.
- Recency: The sale needs to have happened close to the date of valuation. Most appraisers prefer sales within the past three to six months. For tax assessment purposes, some jurisdictions set stricter limits, with sales more than 90 days after the valuation date excluded entirely.
- Size and layout: Square footage, bedroom count, bathroom count, and number of stories all matter. A 1,200-square-foot ranch and a 2,400-square-foot two-story colonial on the same block are not great comps for each other, even though they share a location.
- Condition and age: A fully renovated 1960s home and an original-condition 1960s home will sell at very different prices. Appraisers look for properties in similar overall condition, with comparable updates to kitchens, bathrooms, and major systems.
- Lot size and features: A half-acre lot with a pool commands a different price than a quarter-acre lot without one. Garages, basements, porches, and outbuildings all factor in.
- Zoning and legal use: Properties need to share the same type of permitted use. A residential home and a mixed-use property in a commercial zone are not comparable, even if they look similar from the street.
There are no universal cutoff numbers for how close or how similar a comp must be. The standard is whether the properties are alike enough in character, size, situation, and legally permitted use that a reasonable person would agree they reflect the same segment of the market.
How Adjustments Bridge the Gaps
Perfect comps rarely exist. Almost every comparable sale differs from the subject property in some way, so appraisers make dollar adjustments to account for those differences. If a comp has a finished basement and the subject property does not, the appraiser subtracts the market value of that basement from the comp’s sale price. If the subject has an extra bathroom and the comp does not, the appraiser adds the value of that bathroom.
These adjustments must reflect what buyers in that specific market actually pay for a given feature, not a generic rule of thumb. Fannie Mae’s guidelines make this explicit: an appraiser cannot simply apply a textbook figure like $20 per square foot for size differences when the local market data shows the real adjustment should be $100 per square foot. Each adjustment needs to be supported by market evidence, meaning the appraiser has analyzed local sales data to determine what a particular feature is worth in that neighborhood.
When adjustments are small and few, the comp is strong. When an appraiser has to make large adjustments across many categories, the comp becomes weaker because each adjustment introduces a degree of estimation. Appraisers document their reasoning for every adjustment, explaining the data sources and analysis behind the numbers. A simple statement that “an adjustment was made” is not sufficient under Fannie Mae’s appraisal standards.
Where To Find Comparable Sales Data
Professionals and homeowners access comp data through different channels, but the underlying information comes from the same place: actual recorded transactions.
Real estate agents use Multiple Listing Service (MLS) databases, which contain detailed sale prices, property features, photos, and days on market for virtually every home sold through an agent. This is the most comprehensive source, but MLS access is generally restricted to licensed agents and appraisers.
Homeowners can find comp data through several public and consumer-facing tools. Many county tax administration offices offer online comparable sales search tools that let you look up recent sales in your neighborhood, mapped by location. These pull from the county’s own property records and mass appraisal systems, so they reflect actual recorded deed transfers rather than estimates. Your county assessor’s website is a good starting point.
Consumer real estate sites like Zillow, Redfin, and Realtor.com display recent sale prices for homes in any area. These are useful for a rough sense of market activity, though they may lack the detailed property condition data that a professional appraisal would include. Public records portals maintained by your county recorder or clerk of court also let you search deed transfers, though the interfaces tend to be less user-friendly.
When Comps Fall Short
The comparable sales method works best in active markets with plenty of similar properties changing hands. It becomes less reliable in specific situations.
Unique properties present the biggest challenge. If you own a custom-built home with unusual architecture, a converted church, or a large rural estate, finding truly similar recent sales may be impossible. In these cases, appraisers select the best available sales and make larger adjustments, but the confidence level of the final value drops with each additional adjustment required.
Low-inventory markets create a different problem. When very few homes are selling, appraisers may need to look farther back in time or farther away geographically to find comps, both of which weaken the comparison. In a rapidly appreciating or declining market, even a sale from six months ago may not reflect current conditions, and time adjustments become necessary.
Rapid shifts in interest rates or economic conditions can also make recent comps misleading. A home that sold when mortgage rates were significantly lower may have attracted a higher price than the same home would command today, even if only a few months have passed. Appraisers are expected to account for these market shifts, but doing so requires judgment rather than precise calculation.
How Comps Affect You as a Buyer or Seller
If you’re buying a home, the appraisal based on comparable sales is one of the final hurdles before closing. Your lender orders the appraisal to confirm the home is worth at least what you’ve agreed to pay. If the appraisal comes in below your offer price, the lender may not approve the full loan amount, which means you’d need to make up the difference in cash, renegotiate the price, or walk away.
If you’re selling, understanding comps helps you set a realistic listing price. Overpricing relative to recent comps leads to longer time on market and eventual price cuts. Your agent will prepare a comparative market analysis, which is essentially the same comp-based approach appraisers use, just less formal.
If you’re contesting a property tax assessment, comps are your most powerful tool. Pulling recent sales of similar homes in your neighborhood and showing that your assessed value exceeds what comparable properties actually sold for gives you concrete evidence for an appeal.
Comparable Sales in Business Valuation
The comp concept extends beyond real estate. When valuing a business, analysts use a similar approach called precedent transaction analysis. Instead of comparing houses, they look at what buyers recently paid to acquire similar companies.
The mechanics differ because businesses are valued using multiples rather than raw sale prices. A common approach divides the purchase price (expressed as enterprise value) by an operating metric like EBITDA (earnings before interest, taxes, depreciation, and amortization, which is essentially the company’s operating cash flow). If similar companies recently sold for 8 to 10 times their EBITDA, that range provides a valuation benchmark for the company being evaluated.
Just like in real estate, the result is not meant to be a precise number. It establishes a reasonable range based on what real buyers paid for comparable assets in the real market. The quality of the analysis depends entirely on how comparable the selected transactions actually are.