The renovation budget that drifts the same way every time

Look at enough renovation budgets against what they actually cost and a pattern shows up that has nothing to do with the homeowner or the contractor. Kitchens tend to land close to estimate, sometimes under. Bathrooms almost always run over, usually by a few hundred rather than a few thousand, but reliably so.

That is odd, because a bathroom is smaller and simpler than a kitchen. It should be the easier number to get right.

Why the small room is the one that slips

A kitchen quote gets scrutinised. Cabinets, worktop, appliances: every line is a real product with a real price, checked against two or three suppliers before anyone commits. A bathroom quote gets treated as a rounding error next to it, so it gets less attention, and less attention is exactly where estimates go soft.

Tiles are the usual culprit. The estimate uses a mid-range price per square metre. The homeowner, standing in the showroom months later choosing between three tiles that all looked the same in a spreadsheet, picks the one that does not. Multiply that gap by a bathroom's worth of floor and wall and it is a few hundred pounds before anyone decided to overspend.

What is actually behind the wall

The other reliable overrun is anything behind existing plaster or under an existing floor. Rewiring, old pipework, subfloor damage: none of it is visible at quote stage, all of it is common in anything built before the last renovation, and the contingency for it gets treated as padding rather than a real cost, which is backwards.

Five percent contingency on a job where everything is visible is reasonable. Five percent on a seventies bathroom with pipework nobody has looked at since is a bet, and it is worth naming as a bet rather than pretending the number covers it.

The column that matters more than the total

Total budget tells you what you planned to spend. It does not tell you where the plan was wrong, and if you do not know where it was wrong you will make the same estimate next time.

Estimated against actual, by category, is the thing worth keeping. Not to assign blame; the contractor is not usually the reason a tile choice changed. It is to notice, category by category, which ones you consistently underestimate, so the next bathroom quote gets a heavier contingency than the next kitchen quote, instead of the same flat percentage applied to both because that is what the template says to do.

The renovation that stayed on budget

The homeowners who come in close to plan are not the ones who chose cheaper finishes. They are the ones who picked their tile, their tap, their worktop before the quote was final, not during the build. Every decision made mid-project costs more than the same decision made on a Tuesday afternoon with three tabs open and no plumber waiting on an answer.

That is the whole trick, and it costs nothing to use. Decide early. Price what you decided. Save the contingency for the wall you cannot see, not the tile you have not chosen yet.