The earlier a project has a credible cost plan, the fewer surprises it carries into tender.

Most cost overruns are not the result of a single bad decision — they accumulate from a string of small, unpriced assumptions made before design freeze. A robust cost plan at RIBA Stage 2 forces those assumptions into the open early, when changing course is still cheap.

The practical discipline is simple to describe and harder to hold to: benchmark against comparable schemes, price risk explicitly rather than folding it into a contingency line, and revisit the plan at every design gate rather than only at tender. Clients who insist on that rhythm consistently see fewer late-stage value-engineering exercises — because the hard choices were already made when they were still choices, not damage control.