# How to Compare Builder Quotes Without Missing Hidden Costs > Compare builder quotes like-for-like: exclusions, provisional sums vs PC sums, and contingency — then use the free checklist before you appoint. Author: Ben Murrell, Homeowners Project Manager · Published: 2026-04-18 · Category: Budgeting Canonical: https://www.homeownersprojectmanager.co.uk/blog/how-to-compare-builder-quotes You've done the sensible thing and got three quotes. They range from £85,000 to £140,000 for what's supposedly the same extension. Which one is right? Often, none of them — because they're not actually quoting for the same job. ## Read the exclusions first The cheapest quote is usually cheap because of what's missing, not because the builder is more efficient. Look for the exclusions list before you look at the total. Common items left out entirely: external drainage connections, structural steel supply (sometimes only the installation is priced), scaffolding, skip hire, building control fees, and making good to the rest of the house once the extension connects to it. ## Provisional sums are a placeholder, not a price "PS £2,000 for kitchen electrics" isn't a quote — it's a guess, and it's almost always a low one designed to make the headline number look better. Ask for every provisional sum to be justified, or better, replaced with a firm price once the scope is actually known. ## Check the specification, not just the total Two builders can both say "aluminium bifold doors" and mean very different things — a budget system versus a premium one can differ by thousands per opening. The same applies to insulation standards, flooring, and kitchen allowances. Ask for the actual product or an allowance figure per item, not just a category. ## Where trade pricing changes the comparison Materials are one of the biggest swing factors between quotes, and one of the easiest to get wrong when comparing on paper. A builder pricing a kitchen or bathroom "supply and fit" is usually including their own margin on top of retail — sometimes 15–20%. Where a project manager can source materials directly at trade prices instead, that markup disappears, and a quote that looked mid-table on paper can end up the cheapest in practice once it's compared fairly. ## Provisional sums, PC sums and contingency — read these before the total - **Deep dive:** [provisional sums & PC sums in builder quotes explained](https://www.homeownersprojectmanager.co.uk/blog/provisional-sums-pc-sums-builder-quotes-explained). For client-held buffer sizing (separate from PS/PC), see [how much contingency for a UK renovation or extension](https://www.homeownersprojectmanager.co.uk/blog/how-much-contingency-renovation-extension-uk). - **Provisional sum (PS):** a placeholder allowance where scope or price is not yet firm — treat as risk, not a firm price; demand what it covers and when it will be firm. - **PC sum / prime cost:** often an allowance for a defined supply item (e.g. sanitaryware) before final selection — different from a vague PS dumping ground; still check margin and fitting labour. - **Do not compare headlines until PS/PC rows match** across tenders (same description, same assumption). - **Contingency is yours, not the builder's gift:** hold a separate client contingency % against works; do not assume leftover PS equals contingency. - **Ask in writing:** what converts a PS to a firm price, who owns overrun on that line, and what is excluded entirely. - **Next step:** download or print the [builder quote comparison checklist](https://www.homeownersprojectmanager.co.uk/resources/builder-quote-comparison-checklist) (Sheet / printable) and line up PS, PC, steels, drainage, scaffold and making-good **before** totals. For budget structure, use the [extension / loft budget planner](https://www.homeownersprojectmanager.co.uk/resources/extension-loft-budget-planner). ## The real comparison A proper like-for-like comparison means the same specification, the same exclusions made explicit, and the same contingency treatment across every quote. That's a few hours of careful reading — or it's the first thing I do when I review quotations for a client, before a single trade is appointed. Still building your shortlist? [How to find a good builder in London](https://www.homeownersprojectmanager.co.uk/blog/how-to-find-a-good-builder-london) covers where good builders come from and how to run a tender they want to price. Printable version: use the [builder quote comparison checklist](https://www.homeownersprojectmanager.co.uk/resources/builder-quote-comparison-checklist) to line up exclusions, provisional sums, steels, drainage, scaffolding and making-good across every quote before you look at the totals. To see what the winning quote is likely to cost you by the end, run it through the [extension cost overrun calculator](https://www.homeownersprojectmanager.co.uk/resources/extension-cost-overrun-calculator). If you would rather someone else did the comparison, email me the quotes for a free line-by-line review, and [what a project manager costs](https://www.homeownersprojectmanager.co.uk/project-manager-cost) explains my fee if you want more than that. **Sense-check the totals:** before the quotes arrive, the [extension cost calculator](https://www.homeownersprojectmanager.co.uk/resources/extension-cost-calculator-london) and [loft conversion cost calculator](https://www.homeownersprojectmanager.co.uk/resources/loft-conversion-cost-calculator-london) give a sourced London build range to hold them against. --- Homeowners Project Manager — independent client-side project management for homeowners in South West London. Contact: 07525 474 849 · https://www.homeownersprojectmanager.co.uk/contact