Marginly
Free — no signup required

Free Property Development Appraisal Calculator

Calculate profit, SDLT, development finance costs and margin on GDV for any UK property development deal. Fully free, no login needed.

1Purchase & Acquisition
£
£
%
Purchase price£250,000
SDLT£15,000
Legal fees£3,500
Broker fee£2,500
Total Acquisition£271,000
Estimated Profit
£-58,196
High Risk-12.9%on GDV
ROI
-11.5%
On Cost
-12.4%
Cash In
£140,772
Total Costs
£508,196
Cost Breakdown
Acquisition£271,000
Build£198,240
Finance£29,956
Selling£9,000
Total£508,196

Save this deal

Create a free account to save deals, compare scenarios, and track your project from start to finish.

Sign up free — no card needed

How to use this property development calculator

This free property development appraisal calculator covers all four stages of a development deal: purchase and acquisition costs, build costs, development finance, and the sales exit.

Purchase section: Enter the purchase price and the calculator automatically applies the correct 2025/26 SDLT rates, including the 5% additional dwelling surcharge if applicable. Add your legal fees and broker fee to get total acquisition costs.

Build section: Choose your project type (light refurb, heavy refurb, conversion, or new build) to get typical cost ranges. Enter your build area in m² and cost per m². Add contingency (typically 10–15%) and professional fees (architect, structural engineer, QS).

Finance section: Model development finance costs including LTV, monthly interest rate, arrangement fee, exit fee, and loan term. The calculator assumes interest on 60% average drawn balance, which is typical for staged development finance.

Exit section: Enter your GDV (Gross Development Value — the expected total sale price) and selling costs (estate agent fees, legal, marketing). The calculator shows gross profit, margin on GDV, ROI, and profit on cost.

What is a good margin on GDV?

Most experienced developers target a minimum of 20% margin on GDV for a development deal to be considered viable. Between 15–20% is considered decent but tight. Below 15% is high risk, especially on longer projects where costs can escalate. Marginly colour-codes the result so you can see at a glance whether a deal stacks.