Cost overrun is the thing homeowners regret most, and the commonest cause of a fight with a builder is not late payment but work nobody agreed to in writing. Both come from the same place: a scope that was never written down properly and a budget that only counted the build.
Pick what you are doing. This gives you a range, the costs that sit outside a builder's quote, and a written scope you can send to three of them so the answers come back comparable. Nothing is uploaded and it runs in your browser.
These are the ones people find out about later. Not every one will apply to you, but each is triggered by something you have picked or by the age of the property.
On a property built 1945 to 1979, that is about £5,438 set aside and not spent on anything you can see. Asbestos is very likely. Artex ceilings, garage roofs and floor tiles are the usual places.
The commonest budgeting mistake is leaving this out entirely. A contingency is not optional spending, it is spending you have not identified yet. If you finish without using it, you have a kitchen island. If you never had it, you have a half finished job and a difficult conversation.
Three quotes written to three different assumptions cannot be compared, which is how people end up picking the one that quietly left things out. This produces a scope with the same questions for everybody, including whether VAT is in the number and what happens if the scaffold stays up longer than planned.
The commonest cause of a dispute with a builder is not late payment. It is work that changed partway through and was never written down. Forty eight per cent of contractors who have payment disputes name unforeseen cost and scope change as the trigger, ahead of clients who will not pay.
Both sides remember the conversation differently six weeks later. Whoever wrote it down at the time is the one who is right.
Most of our work is tracking money that leaves in ways nobody wrote down at the start. A renovation turns out to be the same problem in a different costume. There are more free tools for homeowners, and rather more for businesses.
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Cost ranges are indicative figures drawn from published UK guides for 2026, which disagree with each other considerably. A kitchen is quoted anywhere between five and eighty five thousand pounds across sources depending on what is counted. Treat these as a starting point for a conversation rather than an estimate of your job, and get quotes from builders who have seen the property. This is not a quotation, a valuation or professional advice. Whether you need planning permission, building regulations approval or a party wall award depends on your specific property, and those should be confirmed with your council, an approved inspector or a surveyor rather than with a calculator.
VAT is the biggest and the most commonly missed, since a quote may be shown excluding it. Then contingency, architect or designer fees at five to twelve per cent of build cost, structural engineer calculations, Building Control fees, planning application fees, a party wall surveyor where work affects a shared wall, asbestos survey on anything built before 2000, scaffold, skip and parking permits, and somewhere to live if the property is uninhabitable. Furnishing the finished result is regularly a five figure sum that nobody budgets for.
Ten per cent on a property built after 2000, rising to around twenty per cent on anything from before 1919. Older properties hide more: joists, wiring, damp, drainage and lath and plaster that cannot simply be skimmed over. The commonest budgeting mistake is leaving contingency out entirely, which does not remove the cost, only the plan for meeting it.
Because they count different things. A kitchen is quoted anywhere between five and eighty five thousand pounds across published UK guides, depending on whether the figure includes appliances, worktops, electrics behind the units, flooring, plastering and fitting, and on the specification assumed. Any single number is meaningless without knowing what sits inside it, which is why comparing quotes on inclusions rather than totals matters more than comparing calculators.
Potentially, where work affects a shared wall, involves excavation near a neighbouring property, or cuts into a party structure. You serve notice and the neighbour may consent or dissent. If they dissent, you generally pay for their surveyor as well as your own, so budget for two at one to three thousand pounds each. Serving notice early and properly is the cheapest way to stop this escalating. Whether it applies to your specific job should be confirmed with a surveyor.