Comparable Adjustment Calculator
Adjust a comparable sale price for size, condition, features and market movement to estimate what a different property is worth.
💼 Are you a real estate agent or broker? Send this calculator to your buyers on your own branded listing page — every enquiry comes straight to your WhatsApp. Create free agent page →Valuation by comparison is the method most sales actually use, and the adjustments are where it succeeds or fails. A comparable is never identical: it is bigger or smaller, better or worse, has parking or does not, and it sold at a different point in the market.
Making each adjustment explicitly, with a number attached, produces a figure you can defend to a seller or a buyer. Doing it in your head produces a figure you cannot.
How adjustments work
Start from the comparable sale price and adjust toward your property. Extra floor area is valued at a marginal rate, not the average price per unit, because the second bedroom is worth less per unit than the first. Condition and features are money amounts, and market movement is applied to the original price across the months since it sold.
Worked example
A comparable sold at 385,000 with 1,150 square feet. Your property has 1,280 — 130 more at a marginal 200 gives 26,000. It is in worse condition, so deduct 15,000, but it has parking the comparable lacked, so add 8,000. The sale was five months ago in a market moving 0.3% a month, adding 5,775. The adjusted value is 409,775.
Use the marginal rate, not the average
Dividing a sale price by its floor area gives an average that includes the land, the kitchen and the bathroom. Extra space is worth considerably less per unit than that average, so using it inflates the adjustment on any size difference.
Turn a calculation into an enquiry
Buyers who run these numbers are ready to talk. Give every listing its own page with your photo, phone and WhatsApp on it — leads land straight on your phone.
Create your free property pageFrequently asked questions
How many comparables should I use?
At least three, adjusted independently, and look at the spread. Three adjusted figures clustering within a few percent is a reliable valuation; three that scatter widely mean the comparables are not comparable enough.
What marginal rate should I use for extra space?
Typically well below the average price per unit area — often half to three quarters of it. Derive it by comparing two otherwise similar properties of different sizes in the same area rather than assuming a figure.
How far back can a comparable be?
Six months is usually the practical limit, less in a fast-moving market. Beyond that the time adjustment becomes larger than the adjustments you are confident about, which undermines the whole comparison.