Provisional Sums and Contingencies: Two Different Safety Nets

These two terms get used interchangeably in casual conversation, but they protect against different things, and a budget that doesn't distinguish between them will eventually be drawn down twice by the same risk.

A provisional sum is an estimated allowance for work that is known to be required but isn't yet designed in enough detail to price firmly: sanitary fittings before a client has chosen a supplier, landscaping before a layout is finalised. It will be adjusted once the work is defined, but it is not a risk allowance; it's a placeholder for a real cost that simply hasn't been specified yet.

Contingency is the allowance for genuinely unforeseen events: ground conditions that differ from the site investigation, a regulatory requirement that changes mid-project, a price shock in a key material. A well-run project draws down contingency reluctantly and tracks every drawdown against a specific cause, because once contingency is exhausted, every further risk lands directly on the client or the contractor with no buffer left to absorb it.

If your cost reports lump these together, you lose the ability to tell whether your project is running into design uncertainty (provisional sums) or genuine bad luck (contingency), and those require different responses. One is solved by finalising design decisions faster; the other is solved by better risk allowance at the outset.