Cost and Budget: A Baseline to Measure Spend Against
Without a cost baseline, there is no reference to measure overrun.
- Cost baseline — Cumulative planned spend
- Actual spend — What was actually spent
- Contingency reserve — A margin for known risks
Cost management estimates the work costs and aggregates them into an approved budget that becomes the cost baseline against which performance is measured. It moves from estimating activity costs, to aggregating them into a budget, to controlling spend against the baseline. The budget includes a contingency reserve to face known risks. Exceeding the baseline is a warning that calls for analysis and correction.
Omitting a contingency reserve from the budget. A realistic budget includes a reserve for known risks.
Aggregate estimates into a budget, and measure spend against it.
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Cost management turns component estimates into an integrated budget that governs project spend. It starts by estimating activity costs, then aggregating them into a cost baseline that represents cumulative planned spend over time, often drawn as an S-shaped curve. A contingency reserve is added on top of the baseline for known risks, and a management reserve at a higher level for the unforeseen. In execution, actual spend is compared against the baseline to detect overrun early and take corrective action. Linking this control to earned value gives a more accurate picture of project health in both cost and schedule.
Frequently asked questions
What is the cost baseline?
The approved budget distributed over time, the reference for measuring cost performance.
What is the difference between contingency and management reserve?
Contingency covers known risks within the baseline; management reserve covers the unforeseen outside it.
How do I know a cost overrun?
By comparing actual spend to the baseline, or a cost performance index below 1.
Why does the budget curve look like an S?
Because spend is slow at the start and end and accelerates in the middle.
How is spend estimated for the budget?
By estimating activity costs then aggregating them bottom-up into a budget.