Comp Radius: How Far Is Too Far?
The search radius you use for comparable sales can make or break your analysis. Too narrow and you won't find enough data points. Too wide and you'll include properties from different markets that don't reflect your subject property's value. Getting the radius right is one of the first decisions in any comp analysis, and it depends entirely on market density.
The density principle
The right comp radius is determined by one factor: how many comparable transactions occur per square mile. Dense urban areas generate dozens of sales per month within a small radius. Sparse rural areas might produce one or two sales per year within the same radius.
Your goal is to find 3-5 good comps within the tightest radius possible. Start narrow and expand only as needed.
Starting radius by market type
| Market Type | Starting Radius | Max Expansion |
|---|---|---|
| Urban (dense city) | 0.25 miles | 1 mile |
| Suburban (subdivisions) | 0.5 miles | 2 miles |
| Exurban (sparse suburban) | 1 mile | 5 miles |
| Rural | 3 miles | 10-15 miles |
| Remote rural | 5 miles | 20+ miles |
These are starting points. The actual radius you need depends on the specific location and how active the market has been recently.
When tighter is better
In subdivisions, the tightest possible radius often gives the best results. Properties within the same subdivision share the same HOA, builder quality, lot sizes, and neighborhood amenities. A comp from the same subdivision is almost always better than one from a different subdivision 2 miles away, even if the distant comp is more similar in square footage.
In urban areas with block-by-block value changes, even half a mile can cross into a different micro-market. Properties on one side of a major road might be worth 20% more than properties on the other side. Your comp analysis tool should show these locations on a map so you can visually verify that comps are in the same micro-market.
When wider is acceptable
Expanding your radius becomes necessary and acceptable when:
- Fewer than 3 comps at the starting radius: You need a minimum number of data points for a reliable analysis. Three is the floor.
- Same school district: If the expanded radius stays within the same school district, the comps remain relevant because school quality is a primary value driver.
- Same property type is rare: If your subject is a multi-family property and there are few multi-family sales nearby, expanding is necessary. See our guide on how to comp multi-family properties.
- Price point is unusual: Luxury or very low-price properties sell less frequently, requiring a wider net.
- Market is slow: In a market with few transactions, wider radius is the alternative to extending the time window.
Natural boundaries that override distance
Raw distance isn't the only factor. Natural and man-made boundaries create value breaks that matter more than miles:
- Highways and interstates: A major highway can divide neighborhoods with 10-20% value differences
- Railroad tracks: Historic value boundary in many cities
- Rivers and waterways: Properties on different sides of a river are often in different markets
- School district boundaries: The most impactful boundary for residential values. See our guide on school districts and property values.
- Flood zone boundaries: Properties in and out of flood zones are effectively in different markets
- City/county lines: Different tax rates and services on each side
- HOA boundaries: HOA versus non-HOA areas have different buyer pools
A comp 0.5 miles away but across a school district boundary might be worse than a comp 1.5 miles away in the same district.
The direction of expansion matters
When you expand your radius, don't expand equally in all directions. Expand toward similar neighborhoods and away from dissimilar ones. If your subject is in a quiet residential area and there's an industrial zone to the east, expand west, north, and south but not east.
Think about where buyers cross-shop. A buyer looking at your subject property would also consider which other neighborhoods? Those are the directions to expand your comp search.
Radius versus time: which to expand first
When you can't find enough comps, you have two options: expand the radius or extend the time window. In most situations, expanding the radius slightly (within the same market) produces better results than going back further in time.
A comp from a similar neighborhood that sold 2 months ago is generally more useful than a comp from your exact neighborhood that sold 10 months ago. Market conditions can shift significantly over time, but a well-chosen comp from a similar nearby area reflects current pricing.
Exception: in rapidly changing markets (strong appreciation or decline), a closer but older comp needs a larger time adjustment, and a farther but recent comp might actually be more reliable if the neighborhoods are comparable.
Red flags: you've gone too far
Signs that your comp radius is too wide:
- Adjusted comp values have a wide spread: If your 5 comps produce adjusted values ranging from $200K to $310K, some of those comps are from different markets
- You're crossing multiple school districts: The comps are no longer in the same buyer market
- Price per square foot varies by more than 30%: This indicates fundamentally different market areas
- You're including different housing stock: Mixing 1960s ranch-style neighborhoods with 2010s new construction subdivisions
- Total adjustments exceed 20%: The comp needs too many adjustments to be useful, which often happens when it's from a different market area
Using technology to optimize radius
Deal Run's comp analysis lets you adjust the search radius interactively and see results update in real-time on a map. Start at the tightest radius, review what's available, and expand gradually until you have 3-5 solid comps. The map view lets you visually confirm that all comps are in comparable locations before you include them in your analysis.
The ARV calculator also flags when comps are outside typical radius ranges for the market type, helping you catch over-expansion before it skews your analysis.
Quick reference: radius decision tree
- Set starting radius based on market type (see table above)
- Search for comparable sales within the last 6 months
- Found 3-5 good comps? Stop here.
- Found fewer than 3? Expand radius by 50% increments
- At each expansion, check for boundary crossings (school district, highway, flood zone)
- If expanded radius still doesn't yield 3 comps, extend the time window to 9-12 months before expanding further
- If you've expanded beyond the maximum and extended time to 12 months with fewer than 3 comps, use alternative valuation methods (see when comps don't exist)
Related articles
- How to Run Comps Like a Pro
- How to Comp Rural Properties
- Comp Adjustments: A Practical Guide
- MLS vs Public Records for Comps