The all-in cost is what matters, not the purchase price
Every yield, discount and equity calculation is only as accurate as the total cost figure behind it. Using the headline purchase price alone routinely overstates a deal by 8–12% once every transaction cost is included — enough to turn a genuinely good deal into an average one on paper, or worse, mask a bad one.
Stamp Duty Land Tax
SDLT applies on a banded basis, and the additional-property surcharge adds a flat percentage on top for any purchase that isn't replacing your only residence — which covers most investment purchases. This is frequently the single largest cost after the purchase price itself, and the one most likely to be forgotten in a quick mental calculation.
Legal, survey and completion costs
Solicitor's fees for the purchase, a proper survey (not just a mortgage valuation, which isn't a structural survey), and for auction purchases specifically, a buyer's premium and legal pack review. None of these are optional, and none of them are refundable if the purchase falls through.
Finance costs during the project
Bridging or mortgage interest accruing from completion until the property is either let or refinanced onto a standard mortgage, plus any arrangement and exit fees on the finance itself. This cost compounds the longer a refurbishment takes — which is exactly why realistic project timelines matter as much as realistic trade quotes.
Put it all in one place before you offer
Purchase price, plus SDLT, plus legal and survey fees, plus refurbishment with contingency, plus finance costs for the project period, equals your genuine all-in cost. Compare that — not the purchase price — against realistic market value to know whether a deal is actually below market once every real cost is accounted for.