Gross development value, or GDV, is the first number in every development appraisal. Get it right and everything downstream follows. Get it wrong and every other figure in the appraisal is wrong with it.
We calculate GDV for every conversion project we assess, so this guide explains the method we use. It covers the formula, how to find reliable comparables, a worked example with round numbers, and the mistakes we see most often.
The maths is simple. The discipline is not. Most bad appraisals fail on optimistic values, not on arithmetic.
What GDV is and why it drives everything
GDV is the total market value of a completed scheme. For a sales scheme, it is the sum of what every unit would sell for at today's prices. For a rental scheme, it is the capital value of the completed, let building.
Three things make GDV the anchor of any appraisal. First, lenders size development loans as a percentage of GDV, so it sets how much you can borrow. Second, developer profit is normally measured against it. Third, the maximum price you can pay for a building falls straight out of it, through the residual method described below.
A £50,000 error in build costs hurts. A 10% error in GDV can sink a project entirely, because it moves the whole value side of the appraisal at once.
The formula
The GDV calculation itself is addition.
GDV = the sum of the end values of every unit in the scheme.
For a conversion producing flats for sale, that means pricing each flat from comparable evidence and adding the results together. Nothing is deducted at this stage. GDV is a gross figure, before any costs.
The deductions come next, in the residual land value calculation. This tells you the most you can afford to pay for the building or site:
Residual land value = GDV minus build costs minus fees minus finance and selling costs minus developer profit.
Each line deserves a brief explanation. Build costs cover the conversion works themselves, plus contingency. Our conversion costs article sets out indicative ranges by building type. Fees cover the professional team, surveys and statutory charges, typically 10 to 15% of build cost as an indicative allowance.
Finance and selling costs cover interest on borrowing, arrangement fees, agent fees and legals on the sales. Developer profit is the return the project must generate to be worth doing. On residential schemes, an indicative benchmark is 15 to 20% of GDV, and most lenders will expect to see a margin in that region.
Whatever is left after those deductions is the residual land value. If a vendor wants more than that figure, the deal does not work at your assumptions. That is the whole point of the method.
Getting comparables right
GDV is only as good as the comparable evidence behind it. A few rules keep the numbers honest.
Use sold prices, not asking prices. Land Registry data records what buyers actually paid, and asking prices routinely sit 5 to 10% above final sale prices in a normal market. Building a GDV on asking prices bakes optimism into the appraisal from line one.
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Match the product. A converted flat in a former office is a different product from a new-build flat with a warranty, and both differ from a period conversion. Where possible, use sales of similar conversion stock in the same area.
Match the location tightly. Values can change street by street. A comparable half a mile away in a better postcode is not a comparable, it is a hope.
Keep the evidence recent, ideally from the last 6 to 12 months, and work in £ per sqm so you can adjust between units of different sizes. Then price each unit individually. A ground floor flat facing the car park is not worth the same as a top floor flat with a view, even if they are the same size.
Finally, be conservative. If the evidence supports a range, appraise at the middle or below, not the top. Upside that arrives is a bonus. Upside that is already in the appraisal is a risk.
A worked example
Here is a hypothetical example with round numbers. It is not a real project, and the figures are illustrative only.
Imagine a commercial building that converts to 8 flats: 3 one-bed flats and 5 two-bed flats. Comparable sold evidence supports £175,000 for the one-beds and £255,000 for the two-beds.
- 3 one-bed flats at £175,000 = £525,000
- 5 two-bed flats at £255,000 = £1,275,000
- GDV = £1,800,000
Now the residual calculation, using indicative allowances:
- Build cost including contingency = £1,045,000
- Professional fees and statutory costs = £105,000
- Finance costs = £85,000
- Selling and legal costs = £45,000
- Developer profit at 15% of GDV = £270,000
- Residual land value = £1,800,000 minus £1,550,000 = £250,000
On these assumptions, £250,000 is the most this developer could pay for the building. Pay £300,000 and the £50,000 difference comes straight out of profit, cutting the margin from 15% to around 12% of GDV before anything else goes wrong.
It is also worth testing the sensitivity. If sale values come in 5% lower, GDV falls by £90,000, and almost all of that lands on the residual. That is why we stress-test values in every appraisal rather than relying on a single figure.
Common GDV mistakes
These are the errors we see most often when reviewing appraisals.
- Using asking prices instead of sold prices, which inflates GDV before the appraisal has even started.
- Pricing the gross internal area rather than the net sellable area. You only sell the flats, not the corridors and stairs.
- Using new-build comparables for a conversion product, or evidence from a stronger postcode nearby.
- Pricing every unit at the same figure when floor level, aspect and layout clearly differ.
- Ignoring absorption. Eight identical flats reaching the market at once may need incentives or a longer sales period than the appraisal assumes.
- Building future price growth into today's GDV. Appraise at today's values and treat growth as margin, not as a plan.
- Leaving profit out of the residual calculation, which quietly turns the maximum land price into an overpayment.
None of these mistakes looks dramatic on a spreadsheet. Each one moves the answer in the same direction: towards paying too much.
Try it on your building
The fastest way to understand GDV is to run your own numbers. Our free GDV Calculator lets you enter a unit mix and values for a building and see the GDV and residual position in a few minutes.
For a decision you are going to spend real money on, a calculator is a starting point rather than an answer. Our feasibility package includes a tested layout, a unit schedule, indicative costs and a GDV built from local comparable evidence, so the numbers you act on reflect the actual building rather than a set of assumptions.
Either way, the discipline is the same. Value the scheme honestly, deduct every real cost, insist on a proper profit margin, and let the residual tell you what to pay.
Frequently Asked Questions
What does GDV mean in property development?
GDV stands for gross development value. It is the total market value of a completed scheme, calculated by adding up the end value of every unit at today's prices. It is a gross figure, so no costs are deducted from it.
What is a good profit margin on GDV?
An indicative benchmark for residential schemes is 15 to 20% of GDV, and most development lenders expect a margin in that region before they will fund a project. Simpler, faster projects can sometimes justify the lower end. Treat anything much below 15% as a warning sign that the deal has little room for error.
How do lenders use GDV?
Lenders size development finance as a percentage of GDV, often capping total lending at around 60 to 70% of it, alongside a cap on the percentage of costs they will fund. They will usually instruct their own valuer to check your GDV. If the valuer's figure comes in lower than yours, the loan shrinks, so a realistic GDV protects your funding as well as your profit.
