Comparable sales analysis estimates a property's market value by adjusting the sale prices of recently settled, similar properties to match the subject property. Start by collecting three to five suitable solds, listing the subject property's key attributes and checking the figures against official sold-price records such as Valuer General reports before relying on a figure for a major decision.
TL;DR:
- Favor sales from the past three months; six months can work in slower markets, and expand the date range before widening the search area.
- Base adjustments on local paired sales, and treat any comparable needing adjustments above 10% to 15% of its sale price with caution.
- Give the most similar, recent, least adjusted sales greater weight, and report a value range with a best estimate rather than false precision.
- DIY works for quick checks, but development feasibility, lender appraisals, and thin markets warrant a person’s review of the sales and adjustments.
Table of Contents
- What comparable sales analysis measures and when to trust it
- Step-by-step: how to find suitable comparables
- How to make value adjustments to each comparable
- Reconciling adjusted comparables into a single estimate
- Common mistakes and pitfalls to avoid
- How SiteScope supports comparable sales analysis and development feasibility
- When DIY comps are enough and when to bring in an expert
- Turn your comparable sales analysis into a feasibility decision
- FAQ
- Sources
What comparable sales analysis measures and when to trust it
The method rests on one assumption: recent sales of similar properties in the same market reveal what buyers are actually willing to pay now, which is a better guide to value than an asking price or a formula. It works best in established suburbs with frequent turnover, where several genuinely similar homes have sold in the past few months. It works poorly for one-off properties, acreage, or thin markets where the nearest comparable sold a year ago and three suburbs away.
A trustworthy analysis shows its workings. Look for cited sold-price records rather than estimates, adjustments explained through paired-sales reasoning rather than guesswork, and a date range tight enough that market movement hasn't quietly skewed the numbers.
Step-by-step: how to find suitable comparables
Before searching for comparables, write down the subject property's own facts: property type, bedrooms and bathrooms, floor area, lot size, condition, any renovations and relevant planning constraints. This becomes the yardstick every comparable gets measured against.
- Search official sold-price records first, such as state Valuer General or land registry data, because these reflect settled transactions rather than asking prices.
- Cross-check against agent CMA records where available, since local agents often hold more recent sales than public registries have processed.
- Use property portals and council records as a supplement, not a primary source, filling gaps while official data catches up.
- Apply filter rules: a date range of three months is ideal, six months acceptable in slower markets; start with a tight radius and widen only as far as needed; keep floor area within roughly 20% of the subject; stick to the same property type.
- Verify each candidate: confirm it actually settled, check the settlement date, and rule out concessions, family transfers or other non-arm's-length factors that distort the price.
Pro Tip: When a suburb has too few recent solds, widen the date range before you widen the radius, a property two suburbs away rarely compares as well as one six months older in the same street.
How to make value adjustments to each comparable
Once you have genuine comparables, the raw sold prices still need adjusting for the differences between each comp and the subject property.
- Living area: adjust using a local price-per-square-metre rate rather than a flat dollar figure.
- Bedrooms and bathrooms: apply a dollar adjustment per bed or bath band, based on what similar upgrades have added locally.
- Lot size, parking, pool or view: adjust in dollar terms where the local market shows a clear premium.
- Condition and renovation: adjust for the cost and age of recent work, not just its presence.
- Date of sale: adjust for any market movement between the comp's settlement and today.
Keep each adjustment small and evidence-based rather than a round number pulled from habit. A paired-sales approach, comparing two otherwise near-identical sales that differ in one feature, gives the cleanest evidence for an adjustment's size. Where vacant land sales are scarce, valuers often isolate land value by starting from an improved sale and deducting a depreciated cost of the improvements, a technique set out in Valuer General NSW's paired sales analysis of improved sales.
Pro Tip: If an adjustment exceeds 10 to 15% of the comp's sale price, treat that comparable with caution, large adjustments usually mean it isn't similar enough to begin with.
Reconciling adjusted comparables into a single estimate
With each comparable adjusted, the next job is combining them into one defensible number rather than averaging blindly.
- Closest comparable: lean on the single most similar, most recent sale when one stands out.
- Least-adjusted method: give the most weight to whichever comp needed the smallest total adjustment.
- Simple average: useful only when all comps are genuinely close in similarity and recency.
- Weighted average: weight each comp by similarity and recency, penalising any that needed heavy adjustment.
State the result as a range plus a best estimate, not a single false-precision figure, and keep a short note of why each comp was weighted the way it was. That record is what makes the estimate defensible later, to a buyer, a lender or a planning assessment.
Common mistakes and pitfalls to avoid
A handful of errors account for most unreliable comparable sales analyses.
- Using active or pending listings instead of settled sales, which reflects asking price hope rather than what buyers actually paid.
- Skipping condition adjustments, so a renovated comp gets treated the same as a tired one.
- Leaning entirely on an automated valuation model for a high-value or development decision instead of checking the underlying comps.
- Stretching the date range or the radius far beyond what the market justifies, just to find enough comps.
Each of these quietly inflates or deflates the final number without the analyst noticing, which is exactly why the record of reasoning behind each adjustment matters as much as the adjustment itself.
How SiteScope supports comparable sales analysis and development feasibility
We provide comparable sales lists, adjusted estimate scenarios and planning constraint checks in a unified report, so the comparable analysis sits alongside zoning rules and cost benchmarks rather than as a separate spreadsheet. For a quick headline estimate, our service offers an instant read on a property's zoning and development potential. For decisions where more is riding on the number, our report adds human review of the comparable set, multi-scenario modelling and a reviewed conclusion rather than an automated-only output. Our additional concierge service extends that with a site inspection and introductions to relevant professionals.
When DIY comps are enough and when to bring in an expert
A DIY comparable sales analysis is fine for a quick gut check or a modest transaction where getting the figure slightly wrong isn't costly. Development feasibility, bank appraisal requirements or markets with few genuine sales call for a different standard, because the cost of an inflated estimate is higher. Authoritative sold-price records and a human-reviewed check on the adjustments reduce that risk in exactly those higher-stakes situations.
For negotiation tactics that build on a solid comparable sales estimate, including underquoting red flags and strata-related levers, OptiWealth Insights' guide on house price negotiation covers practical adjustment-related tactics for Australian buyers.
— Ashton
Turn your comparable sales analysis into a feasibility decision
Once you've got a defensible comparable sales estimate, the next question is usually whether a site is worth developing, and that's where a spreadsheet of adjusted solds stops being enough. We offer reports that combine comparable sales work with planning controls, build costs and end value into one feasibility picture, while an additional concierge service adds a site visit and professional introductions for bigger decisions.
Run a free zoning check or view our report options on SiteScope to see how a founder-reviewed analysis compares with a DIY estimate.
FAQ
How accurate is RP data?
RP Data, now part of CoreLogic, draws on official sold-price records and is generally reliable for recent settled transactions, though like any aggregator it can lag behind the primary state sold-price records it's sourced from. For high-stakes decisions, cross-check its figures against the relevant state or territory Valuer General data before relying on them.
What is a disadvantage of using the sales comparison approach?
The method depends on finding enough genuinely similar, recently settled sales nearby, and it struggles in thin markets or with unique properties where few true comparables exist. It can also under-adjust for condition or renovation differences if those adjustments aren't backed by paired-sales evidence.
How do you calculate the sales comparison approach?
List the subject property's attributes, find three to five recent settled comparables, then adjust each comp's sale price for differences in area, bedrooms, bathrooms, condition, parking and date of sale. Reconcile the adjusted figures using a weighted average or the least-adjusted comp to arrive at a final value range and best estimate.
What are some alternatives to RP Data for property data?
Official state and territory Valuer General sold-price records and land registries are the primary authoritative alternative, since aggregator platforms generally source from them anyway. Agent CMA records and council property records can supplement these when official data is still pending for very recent sales.
Sources
The most authoritative figures in Australia come from state and territory Valuer General sold-price records and land or transfer registries, since these reflect settled, registered transactions rather than estimates. Property portals and aggregators are convenient but they generally draw on those same official records with a lag, so cross-check portal figures against the official source when a decision carries real weight.
- Ashfield paired analysis and land valuation (Valuer General NSW)
For established suburbs with limited vacant land sales, valuers commonly isolate land value using a depreciated cost of improvements against a comparable improved sale, a method documented in Valuer General NSW's Northern Beaches valuation report, which shows how this adjustment technique sets defensible local benchmarks.