How Comparable Sales Work
When your county says your home is worth more than it really is, your tax bill gets... ambitious. The fastest, fairest way to nudge it back to reality is with comparable sales ("comps"). This guide shows exactly how comps work, how assessors think about them, and how to build a clean, convincing case for your informal appeal. (New to property tax appeals? Start with our Appeal 101 guide first.)
The 10-Second Version
Comps are recent, nearby arm's-length sales of similar homes. You adjust each sale for differences (size, time, features) to estimate your home's market value on the assessment date. If your adjusted comp value is lower than the assessor's number, you have evidence to reduce your tax basis.
First, Know Your Target: The Valuation Date
Every assessment is tied to a specific as-of date (often January 1 of the tax year). Your comps should bracket that date, capturing sales that closed within 3-6 months of it. If you must reach farther, you'll make time adjustments (more on that below).
Pro tip: If the market has moved, you're not arguing today's price but the value on the assessment date.
What Makes a "Good Comp"?
Think of comps as stand-ins for your home. The closer the match, the less adjusting you'll need.
| Criteria | Description |
|---|---|
| Location | Same subdivision or a tight radius; similar school district, street type, and external influences (busy road, power lines, lakefront). |
| Time | Closest possible to the valuation date. |
| Property Type & Style | Don't compare a 2-story to a ranch if you can avoid it. Match construction quality and age brackets. |
| Size & Layout | Keep GLA (gross living area) within ~15-20%. Bedroom/bath counts should be similar. |
| Lot & Site | Similar lot size/shape, topography, view, corner vs. interior. |
| Condition & Updates | A renovated kitchen, finished basement, or new roof can swing value |
| Arm's-Length | Exclude family transfers, foreclosures, short sales, and sales with outlier concessions. |
Where to Find Comps (Even Without the MLS)
| Source | What You Can Find | How to Access / Tips |
|---|---|---|
| County Property Records | Sales deeds, parcel cards, transfer documents, property characteristics (lot size, square footage, year built), previous sale prices | Visit your county recorder's office in person or online. Many counties offer free parcel search by address. Look for "property appraiser," "tax collector," or "recorder of deeds" websites. Documents may cost $1-5 per page if not freely available. |
| Public Listing Portals | Interior/exterior photos, listing descriptions, feature lists (renovations, appliances, finishes), days on market, original asking price vs. final sale price | Zillow, Redfin, Realtor.com, and Homes.com archive past listings even after sale. Photos help you assess condition and quality compared to your home. Cross-reference listing date with actual sale date from county records. |
| Local Recorder/Assessor Websites | Official sale dates, sale prices, deed transfer stamps, seller/buyer names (to verify arm's-length), mortgage/lien information, legal descriptions | Most counties now digitize these records. Search by address or parcel number. Look for "official records search" or "document search" portals. Verify sale terms: watch for "$0" sales (gifts/family transfers) or "quit claim" deeds (non-market transactions). |
| Neighborhood HOA or Builder Records | Floor plans, model names, standard features by build year, community amenities, original pricing sheets, subdivision plat maps | Contact your HOA management company or check resident portals. Builders often have archived spec sheets. Useful for proving your home matches a comp's layout/finishes exactly - especially in tract developments. |
| Title or Appraisal Reports | Full comparable sales analyses with adjustments, appraiser's notes on market conditions, neighborhood boundary definitions, photos and measurements of comps | If you refinanced or purchased recently, your lender's appraisal is gold. Title company settlement statements show actual sale prices (vs. recorded deed prices with stamps). These reports are already vetted by licensed professionals. |
Rule of three: Aim for 3-6 solid comps. More is not better if quality drops.
Adjusting Comps (Without a PhD)
Appraisers use paired sales to quantify differences. You can do a practical version:
1) Time Adjustment (Market Movement)
Normalize each sale to the valuation date. If prices rose ~6% between the comp's close date and your valuation date, increase older sales by ~6%. If they fell 3%, decrease by 3%.
Simple method: use a credible local trend (median sale price, index, or broker CMA). Keep the math transparent: "+4% time adjustment (Apr->Jan as-of)."
2) Size (GLA)
Larger homes often command a lower $/square foot than smaller ones. Safest approach:
Calculate each comp's $/square foot (living area only), then apply modest adjustments for size differences in dollars, not just by multiplying your $/sf blindly. If two 2,000 sf homes bracket a 1,900 sf subject, you're in the sweet spot - minimal adjustment.
3) Features & Condition
Adjust for meaningful differences only. Below are the most impactful adjustments to consider:
| Feature Category | Details |
|---|---|
| Bedrooms/Baths | Full baths usually add more value than half baths; extra bedrooms matter less than the primary suite quality. |
| Basement/Attic Finish | Finished square footage counts. Distinguish walkout basements (higher value) from standard. Include wet bar, egress windows, quality of finish. |
| Garage Spaces | Count actual enclosed, functional spaces. Carports are worth less. Heated/finished garages add premium. |
| Major Updates | Kitchen/bath remodels (within 5-10 years), new roof (within 5 years), HVAC replacement, new windows, flooring. Check permit records. |
| Externalities | Busy road (traffic counts >10k/day), backing to commercial/industrial, power lines, airport noise, premium views (water, mountain, golf course), cul-de-sac vs. through-street. |
| Lot Size/Features | Significant differences in usable lot size, topography (flat vs. steep), landscaping maturity, privacy (wooded vs. open), corner vs. interior lot. |
| Pool/Outdoor Features | In-ground pool, hot tub, outdoor kitchen, deck/patio size and quality, screened porch, landscaping/hardscaping. |
When in doubt, stay conservative. Your goal is credibility - assessors weigh this heavily, as we explain in our guide on what assessors actually care about.
How to Decide the Right Amount of Adjustments
The hardest part of comp analysis isn't finding differences - it's quantifying them. You have three main approaches, each with different credibility levels:
1. Paired Sales Analysis (Gold Standard): Find two sales that are identical except for one feature, then use that difference as your adjustment. Example: Two homes on the same street, same year, same size - one has a finished basement, one doesn't. The price difference ($18,000) becomes your basement adjustment. This is the most defensible approach because it's market-derived and specific to your neighborhood, but it requires research and perfect pairs are rare. Use this for major features (basement, garage, renovations) if you can find the pairs.
2. Cost-Based Adjustments (Acceptable): Use depreciated construction costs as a proxy. If a finished basement costs $40/sf to build and is 10 years old, you might apply 70% of replacement cost = ~$28/sf adjustment. This approach is logical, transparent, and easy to document, but remember that cost does not equal value - a $30k pool might add only $15k in some markets. Use this when paired sales aren't available, and always disclose your methodology.
3. Rule-of-Thumb Adjustments (Use Sparingly): Industry conventions like "$5k per bedroom" or "$10k per garage bay." These are market-dependent and can feel arbitrary. While they're simple and widely recognized, they offer weak justification and assessors may challenge them. Use this approach only for minor items (half bath, fireplace) where precision isn't critical.
Practical Tips for Setting Adjustment Amounts
Start with $/square foot as a baseline. If comps are selling at ~$270/sf, 100 sf of GLA difference is approximately $27,000 (then shade down slightly since marginal sf are worth less).
Use listing descriptions for clues. If multiple listings highlight "renovated kitchen" as a selling point and those homes sold $15k-$25k higher, that's your range.
Check contractor quotes (even online estimators) for improvement costs, then cut them by 30-60% to reflect contributory value vs. replacement cost.
Scale to your market. A 3-car garage adds more value in a $700k neighborhood than a $250k one. Adjust proportionally.
Document everything. If you're using paired sales, cite the parcel IDs. If you're estimating, explain: "Based on local remodeling costs of $X/sf x 400 sf basement x 50% contributory value."
The "Net Adjustments" Sanity Check
If your total net adjustment on any comp exceeds 15-20% of the sale price, it's not a good comp - find a closer match. Assessors will discount heavily adjusted sales because each adjustment layer compounds uncertainty. Understanding what assessors truly care about helps you prioritize the right evidence.
An Example Comp Grid (What It Should Look Like)
Table 1: Property Characteristics
| Item | Subject | Comp 1 | Comp 2 | Comp 3 |
|---|---|---|---|---|
| Sale Date / Price | - | 6/15 - $540,000 | 3/10 - $520,000 | 8/30 - $560,000 |
| Distance | - | 0.3 mi | 0.6 mi | Same street |
| Style / Age | 2-story / 1998 | Match | Match | Match |
| GLA (sf) | 2,000 | 1,900 | 2,060 | 2,120 |
| Beds / Baths | 3/2.5 | 3/2.5 | 4/2.5 | 3/2 |
| Basement | Finished 400 sf | Unfinished | Finished 300 sf | Finished 600 sf |
| Garage | 2-car | 2-car | 2-car | 3-car |
Table 2: Adjustments & Final Values
| Adjustment Type | Comp 1 | Comp 2 | Comp 3 |
|---|---|---|---|
| Time | +2% | +5% | 0% |
| GLA | +$5,000 | -$3,000 | -$6,000 |
| Beds/Baths | $0 | -$10,000 | +$5,000 |
| Basement | +$15,000 | +$3,500 | -$7,000 |
| Garage | $0 | $0 | -$8,000 |
| Net Adjustment | +$20,000 | -$9,500 | -$16,000 |
| Adj. Sale Price | $570,800 | $536,500 | $544,000 |
Indicated Value (Mean/Median): ~$547,000
You don’t need perfect precision. You need reasonable, well-explained adjustments that triangulate lower than the assessor’s value.
Common Red Flags (What Assessors Discount)
Assessors will discount out-of-neighborhood sales when good local comps exist. They'll also flag distressed or non-arm's-length transactions, sales with wildly different lot sizes, ages, or styles, and any cherry-picking of only the lowest sales while ignoring better matches. Don't forget time adjustments when the market moved.
Avoiding these mistakes is crucial - sloppy comp analysis is one reason some appeals fail. For more on common misconceptions about what makes a strong appeal, see our myths guide.
How Many Adjustments Is Too Many?
If you're adjusting everything, it's not a good comp. Prioritize: 1) Location, 2) Time, 3) Size, 4) Condition, 5) Extras.
If a comp needs major surgery on #1-#3, drop it.
What If You Have Zero Perfect Comps?
Widen the time window and rely on a transparent time adjustment. Step down a "tier" (e.g., similar home one neighborhood over) and add a location adjustment with a brief rationale. Use paired logic: If two nearby sales show $15k premiums for finished basements, you can apply that difference credibly.
Handling Pushbacks (Scripted, So You're Ready)
Assessor: "These sales are older than we prefer."
You: "Understood. I time-adjusted each to the January 1 valuation date using the same market trend applied county-wide. The adjusted prices align tightly at $X-$Y."
Assessor: "This comp is bigger."
You: "Right, which is why I deducted $Z based on paired sales indicating $W per incremental 100 sf in this tract."
Assessor: "We have a newer sale at $___."
You: "Great. If it's arm's-length and similar, let's include it. If it's remodeled or on a premium lot, we should adjust it accordingly."
Quick Glossary (So You Speak Appraiser)
Arm's-Length: A normal, market-exposed sale between unrelated parties.
GLA (Gross Living Area): Finished, above-grade heated area (basements excluded unless finished and typical for the market).
Concessions: Seller credits or incentives that can inflate the recorded price
Sales Comparison Approach: The valuation method you're using; it's king for residential.
Checklist
- Valuation date is clearly stated.
- 3–6 comps within neighborhood/subdivision (or justified otherwise).
- Clear time adjustments.
- Reasonable size/feature adjustments (documented).
- Distressed/non-arm's-length sales excluded.
- Map with distances.
- Photos and sources included.
- One-page executive summary with requested value.
FAQ
Q: Can I use pending or active listings?
They're supporting evidence at best. Closed sales rule the day. This is a common misconception we address in our myths article.
Q: Do I have to reveal interior photos of my home?
Not usually. Describe condition honestly. If you're inferior to typical comps (dated kitchen, original baths), say so.
Q: What if my assessment is capped or limited by law?
You're still arguing market value first. Caps/limits then flow through according to your jurisdiction’s rules.
Final Word (and a Friendly Nudge)
Great comps win appeals because they tell a simple story: "Homes like mine sold for this, around then, and after fair adjustments, my value is here." Keep it clean, conservative, and transparent. (Worried about whether filing an appeal could backfire? We cover that concern thoroughly in our risk guide.)
Sounds like a lot of work? If you'd like a done-for-you comp package tailored to your county, AppealArc can help you assemble and format everything so your informal appeal lands right the first time.