Pulling good comparable sales is only half of a comparative market analysis. The other half is adjustments: the amounts you add to or subtract from each comp's sale price to account for how it differs from the property you are valuing. Get the adjustments right and a handful of imperfect comps converge on a tight, defensible price range. Get them wrong and you can talk yourself into almost any number you like — which is exactly how agents lose listings or leave money on the table. This guide explains the method, the rules that keep you honest, and a full worked example.
Why adjustments exist at all
No two homes are identical, yet you need to compare them on equal terms. A comp that sold for €430,000 with an extra bathroom and a renovated kitchen is not telling you your subject is worth €430,000 — it is telling you a better home sold for that. Adjustments strip out those differences so every comp answers one clean question: "what would this property have sold for if it were as similar to the subject as possible?" Once each comp is adjusted to that common baseline, the prices should cluster, and the cluster is your evidence. If you skipped this step and simply averaged raw comp prices, you would be averaging apples, sheds and swimming pools.
The golden rule: adjust the comp, not the subject
This is where most mistakes start. You are trying to value the subject property, so its price is the unknown — you never touch it. You adjust the comps toward the subject. The direction follows one sentence: superior comp, subtract; inferior comp, add. If the comp has a garage and the subject does not, the comp is superior on that feature, so you subtract the garage's value from the comp. If the subject has a larger garden than the comp, the comp is inferior there, so you add. Write that rule at the top of your worksheet until it is automatic; reversing it inverts every number you produce.
Which features actually move price
You do not adjust for everything — only for differences large enough to change what a buyer would pay. The features that consistently matter:
- Living area — usually the single biggest driver, priced per square metre or square foot.
- Lot or plot size — especially where land is scarce.
- Bedrooms and bathrooms — count and, for bathrooms, quality.
- Condition and renovation — a new kitchen, bathroom or roof versus deferred maintenance.
- Outdoor space and parking — garden, balcony, garage, off-street spaces.
- Location nuance — a quiet street versus a busy road, a view, proximity to a school catchment.
- Energy efficiency — increasingly priced in, as our guide on how to value a house explains.
How to put a number on each feature
An adjustment should reflect a feature's contributory value — what it adds to the sale price — not what it cost to build. A €25,000 kitchen renovation might add only €12,000 to the price; buyers pay for the outcome, not your invoice. The cleanest way to estimate contributory value is paired sales analysis: find two sold homes that are alike in every way except the one feature, and the price difference between them is that feature's value in this market. Two near-identical houses on the same street, one with a garage at €312,000 and one without at €300,000, imply a garage is worth about €12,000 here.
Paired data is not always available, so supplement it with local rules of thumb, cost-to-build figures discounted to contributory value, and a price-per-square-metre benchmark for the area. Whatever your source, be consistent across every comp and conservative on the size of each adjustment. Over-adjusting is how a CMA quietly drifts away from what the market will actually pay.
Keep adjustments within sane limits
Adjustments are a correction, not a rescue. A long-standing guideline from appraisal practice is to keep net adjustments (the total after the pluses and minuses cancel) within about 15 percent of a comp's sale price, and gross adjustments (every adjustment added up regardless of sign) within roughly 25 percent. If a comp needs bigger corrections than that to resemble the subject, it is simply too different to be a strong comparable. The fix is not a bigger adjustment — it is a better comp. This is why choosing the right comparable sales upfront does most of the work; tight comps need only light adjustments.
A full worked example
Suppose you are valuing a three-bedroom house of 110 m² with one bathroom, a small garden and no garage, in average-but-tidy condition. You have three strong sold comps. All figures are illustrative, to show the method rather than any real market.