Cost baseline
The cost baseline (also called the baseline budget) is the construction budget that, once reviewed and authorized, is "frozen" to serve as the benchmark for comparison. All of the project's cost control revolves around it: as work advances, the actual cost incurred is measured against the cost baseline to calculate the variance of each line item and of the project as a whole. Without a fixed baseline, there is no objective way to tell whether the job is over budget or on track.
The defining feature is that the cost baseline is left untouched. If scope changes, extra work items, or price adjustments come up during the job, the original figures are not edited: they are logged as variations or captured in a revised version of the budget, but the baseline is preserved so you can still measure against it. That is why it helps to distinguish the cost baseline (a fixed reference), the current or revised budget (baseline plus approved changes), and the actual cost (what has genuinely been spent).
In practice, the cost baseline usually matches the contracted or awarded budget: on public works it is the contract amount that results from the tender, and on private projects it is the budget the client approves before mobilization. From there, progress payment applications, financial progress, and cost-control reports are always read in relation to that baseline so overruns are caught in time.
Formula
Example
A project has a cost baseline of 10,000,000. At closeout, the actual cost incurred adds up to 10,850,000. The variance is 10,850,000 − 10,000,000 = 850,000 over budget, equal to (850,000 ÷ 10,000,000) × 100 = 8.5% above the baseline.
| Line item | Budget | Spent | Progress | Status |
|---|---|---|---|---|
| Concrete and foundation | $612,000 | $598,000 | On track | |
| Steel structure | $486,000 | $502,000 | Over budget | |
| MEP systems | $398,000 | $240,000 | In progress | |
| Masonry | $354,000 | $160,000 | In progress | |
| Finishes | $520,000 | $70,000 | In progress |
Frequently asked questions
What is the difference between the cost baseline and the project budget?
The project budget is the estimate of the total cost of the project; the cost baseline is that estimate once it has been approved and frozen as the reference point. The project budget is drafted and adjusted; the cost baseline, once set, is not changed and is used to measure actual cost against it.
Why should the cost baseline not be changed?
Because it is the benchmark for comparison: if it were edited every time something changed, you would lose the reference for calculating variances. Scope or price changes are logged separately (as variations or in a current budget), but the baseline is kept intact so overruns and savings can be measured.
How is the variance against the cost baseline calculated?
Subtract the cost baseline from the actual cost: a positive difference is an overrun and a negative one is savings. To express it as a percentage, divide that difference by the cost baseline and multiply by 100. It can be calculated per line item, per work package, or for the whole project.