The first extra purchase on a job rarely looks alarming. A few additional boards, another delivery, an alternative fitting, a replacement after damage. The problem is cumulative: each small change can be reasonable on its own, but the job record may never show whether the estimate, scope or process has changed.
The cost is often more than the invoice line
An additional item may bring delivery, collection time, project delay, waste, a return problem or an external supplier waiting for material. It may also use up stock intended for another job. If the cost is not attached to the job and compared with the original assumption, the business sees busy activity rather than the changed commercial position.
Use a short material-overrun conversation
When a material cost moves, ask:
- Was the original quantity/price assumption wrong, incomplete or outdated?
- Is the change caused by scope, project condition, waste, damage, supplier availability or an internal error?
- Is there a scope change/approval/recovery action—or is it an unrecoverable cost to understand?
- Does the same cause appear on more than one job?
The point is not to assign blame for every extra screw or delivery. It is to identify repeating causes early enough to improve the next price, buying plan or project handover.
An illustrative pattern
Three unplanned £120 purchases are not merely £360 if each also takes a manager's time and delays the next task. The figures are illustrative; the useful discipline is recording the reason at the time, assigning the cost to the job and deciding whether a commercial action is needed.
A simple management example
A £10,000 selling price less £8,000 cost leaves £2,000 profit. An unrecovered extra £500 reduces that profit to £1,500: a 25% reduction. This is a fictional management example, not a tax calculation.
Related FoxSums resources
- Job Costing: Track Project Profit
- Job Margin Calculator
- Scope Change and Additional Work Tracker
- How to Price Jobs and Projects Profitably
Next step
Check the next known overrun against the profit left on the work, not just against the selling price.
Important
General information only. Check the facts and current official guidance for the business’s circumstances.
Sources and review
- Evidence check date: 2 November 2026.
- FoxSums operational guidance. This resource does not make a tax, legal or regulatory determination.