Comparable Adjustment Calculator

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.

Frequently asked questions