GDV vs market value: the difference, and why mixing them costs money

Market value answers: what would a buyer pay for this property today, exactly as it stands, tired kitchen and all? It is the number relevant to the purchase itself: what you should pay, what a bridging lender will lend against at the outset, and what any below-market-value claim must be measured from.

GDV answers a different question: what will a buyer pay for this property once the planned works are complete and it is in its finished, marketable state? It is the number relevant to the project: the flip's sale price, the value a surveyor is asked to support at a refinance after the works, and the figure everything is worked back from in a development appraisal.

Because the questions differ, the same property carries both numbers at once, and the distance between them is not free money. It is the value the works are intended to create, and it has to pay for the refurbishment, the fees, the finance, the risk and the profit before anything is left over.

The practical discipline behind the distinction is that each value is evidenced from its own pool of comparables, and the sorting key is the condition each comparable was in when it sold, which you judge from the original listing photographs. Sales of renovated, finished properties evidence the GDV. Sales of tired, unmodernised properties evidence the as-is market value. The same street can supply both pools, and often does: the done-up terrace that sold in spring speaks to your GDV, while the probate sale three doors down speaks to what you should pay today.

This is why a single blended list of "local comparables" cannot evidence either number properly. Averaging renovated and unrenovated sales gives a figure that sits between the two values and equals neither, flattering the purchase price and understating the finished value, or the reverse, depending on what happened to sell recently. Sort every comparable by condition first, and let each pool answer only its own question.

Rarely by fraud, usually by anchoring. An agent mentions what the renovated house up the road achieved, and that figure becomes the reference point for a property in nothing like that condition. A listing says "potential to add value" and prices some of that potential into the asking price. A buyer walks the street, sees finished houses, and carries their values back to the doer-upper without carrying back the cost of finishing it.

Deal packs institutionalise the error when they are careless or worse: a market value that was actually built from renovated comparables, a below-market-value percentage measured against it, and a purchase that is at full price for its condition dressed as a discount. The tell is always the comparables: if the evidence behind a "current value" is a list of properties that sold refurbished, the number is a GDV wearing the wrong label.

The confusion also runs the other way, more innocently: pricing a GDV from whatever sold nearby, including unmodernised stock, which understates the finished value and can kill a viable project on paper. Both directions are the same mistake, a comparable pool answering a question it was never sorted for.

Overpaying is the first cost. If the purchase is judged against renovated comparables, the margin you think you are buying does not exist: you have paid today for value that only arrives after the works, and the project's profit has been handed to the seller at completion. The deal then only works if everything else goes perfectly, which is not a plan.

The second cost arrives at the valuation. Lenders and their surveyors keep the two numbers rigorously apart: a bridging lender advances against the as-is value at purchase, and a refinance after the works is tested against what the finished property is actually worth, evidenced by finished comparables. An appraisal that inflated either number meets reality as a down-valuation, a funding shortfall, or cash trapped in the deal that the plan said would come back out.

The third cost is subtler: you lose the number that tells you whether the project makes sense at all. The uplift from market value to GDV, minus works, fees, finance and contingency, is the project's created value. Blur the two ends of that calculation and the appraisal can no longer say where the profit comes from, which usually means there is not any.

The fix is procedural, not clever. Record both values explicitly, each with its own comparable pool: the as-is market value from as-is sales, the GDV from finished sales, with the condition of every comparable checked against its original listing. Test the purchase price against the first number only, and the project against the second only. Then require the gap to be explained by the works: if the GDV minus the market value is much larger than the cost of the refurbishment plus fees, finance, contingency and a sensible profit, one of the two values is probably wrong, and it is usually the GDV that is too high.

This is how PropDetect's valuation is built: the GDV comes from comparable sales of properties in finished condition, selected conservatively, with the comparables shown so the basis can be checked rather than taken on trust. The method is documented at /methodology/gdv.