Cost Overrun

Cost overrun occurs when the actual cost of delivering a project exceeds the budget or contract value, reducing margin directly on fixed-fee engagements and damaging forecast accuracy on time-and-materials work.

On time-and-materials engagements, the client typically absorbs overruns through additional billing. On fixed-fee work, the firm absorbs them as a direct reduction to margin. Cost overruns are the largest single cause of margin erosion on project-based engagements.

How overruns happen

Most cost overruns are not surprises. They develop gradually from one or more root causes:

• Scoping gaps: the original estimate did not account for the full complexity of the engagement
• Scope creep: client requests expand the work without a corresponding change order
• Staffing mix drift: senior resources are deployed where juniors were planned and priced
• Estimate optimism: proposals are priced to win rather than to deliver profitably
• No change order discipline: small out-of-scope additions accumulate without ever being formalized

When overruns become visible

The problem with cost overruns is that they are often invisible until they are too large to recover. A project manager who reports “on track” at 60% budget burn and 40% completion is already in a confirmed overrun. Without weekly EAC and burn rate reviews, that signal never surfaces in time to act.

The earliest reliable indicator is the estimate at completion. When EAC first exceeds the contract value, the overrun is still small enough to address through descoping, a change order, or replanning.

Corrective options when an overrun is detected early

1. Descope remaining work to bring EAC back within budget.
2. Raise a change order for work already done or requested beyond the original SOW.
3. Replan remaining delivery with a different staffing mix to reduce cost.
4. Negotiate a budget increase with the client before the project closes.

Each option becomes less viable the later it is exercised. A cost overrun identified at 50% completion can usually be recovered through some combination of these actions. One identified at 95% completion offers almost no options.

Overruns and realization rate

Cost overruns on fixed-fee work depress realization rate at the firm level. Tracking realization by engagement shows which projects are the chronic overrunners and whether the root cause is estimating, scope management, or staffing decisions.