Deal Appraisal
Understanding the inputs and outputs of the Marginly deal appraisal calculator — what each field means and how to use them accurately.
The four sections of a deal appraisal
Marginly's deal appraisal is structured into four sections, each covering a distinct phase of costs. Work through them in order when setting up a new deal.
Section 1: Purchase & Acquisition
Purchase Price
The agreed or expected purchase price for the property or land. This is the starting point for all calculations.
Additional Dwelling (5% surcharge)
Tick this if the buyer (you or your company) owns another property. Almost all development purchases should have this ticked — because you own your own home and/or the company owns other properties. The 5% surcharge applies on top of all standard SDLT bands from the first pound.
SDLT (auto-calculated)
Stamp Duty Land Tax is calculated automatically using 2025/26 rates. The calculation uses banded rates — similar to income tax — applied to the purchase price. SDLT on a £350,000 purchase as an additional dwelling is £22,500 (£12,500 on the first £250,000 at 5%, plus £10,000 on the next £100,000 at 10%).
Legal Fees
Solicitor costs for the purchase. Typically £2,500–£5,000 for a standard residential purchase, more for complex transactions, commercial property, or portfolio purchases. Enter the total fee including VAT if VAT-registered.
Broker Fee
If you used a finance broker to source your development finance, they typically charge 1–1.5% of the facility size. Enter this as a percentage of the purchase price (it defaults to 1% which is a reasonable approximation, but adjust to your actual agreement).
Section 2: Build Costs
Project Type
Select the type that best describes your project. This sets the typical cost-per-m² range shown below the selector:
- Light refurb: £500–£1,000/m² — cosmetic and minor works, no structural changes
- Heavy refurb: £1,000–£1,800/m² — significant internal works, possibly structural
- Conversion: £1,200–£2,100/m² — change of use, e.g. house to flats
- New build: £1,500–£2,800/m² — ground-up construction
Selecting a project type sets the mid-point cost automatically. Adjust to match your actual quotes.
Build Area
Total floor area in square metres (internal GIA — Gross Internal Area). For a conversion, use the post-conversion internal floor area.
Cost per m²
Your total build cost divided by the build area. Get this from your quantity surveyor, contractor quotes, or comparable projects. The project type selector gives you a typical range as a starting point.
Contingency (%)
Applied as a percentage of the build cost. 10% is standard for experienced developers with a well-defined scope; use 15–20% for first-time developers, complex sites, or projects with significant unknowns.
Professional Fees (%)
Applied as a percentage of build cost. Covers architect, structural engineer, QS, building control, planning consultant. Typically 8–12% of build cost on residential projects.
Other Costs
A catch-all for costs that don't fit elsewhere — utilities connections, scaffold hire, skip hire, party wall awards, monitoring surveyor visits, etc.
Section 3: Development Finance
LTV (%)
Loan to Value as a percentage of total project costs. Typical development finance LTV is 60–75%. The loan amount is calculated as total project cost × LTV%.
Monthly Interest Rate (%)
The monthly interest rate charged on the drawn development finance. Typical rates are 0.7–1.1% per month. Interest is calculated on 60% of the facility size (representing typical average drawn balance on a staged drawdown).
Arrangement Fee (%)
Charged by the lender at drawdown, expressed as a percentage of the facility size. Typically 1.5–2.5%.
Exit Fee (%)
Charged on repayment of the loan. Typically 1–2% of the facility size.
Finance Term (months)
The length of the loan in months. For most residential development projects, 12–18 months is typical. Longer projects (new build or complex conversions) may need 18–24 months.
Section 4: Sales & Exit
GDV (Gross Development Value)
The total expected sale proceeds from the completed project. For a multi-unit scheme, this is the sum of all sale prices. Use comparable sold prices in the immediate area — not asking prices, which are typically 2–5% above achieved prices.
Selling Costs (%)
Applied as a percentage of GDV. Covers estate agent fees (0.75–1.5% + VAT), legal fees for the sale, and marketing costs. Typically 2–3% in total.