How to Control Cost and Schedule Variances During Construction

Controlling a construction project is not just a matter of comparing invoices with the budget or checking whether planned tasks have been completed. To identify problems in time, the company needs to link cost, physical progress, and schedule, while also taking into account commitments already made to suppliers and subcontractors. This makes it possible to distinguish between an expense that has not yet been invoiced and a variance that already affects the expected cost of the project.

Establish a baseline that allows comparison

Monitoring starts with an approved baseline: the budget and schedule against which performance will be assessed. It is advisable to break them down by cost items or work packages, with identifiable people responsible, milestones, and dates. If the plan contains only overall totals, it will be difficult to pinpoint which activity explains a variance.

The baseline should be kept separate from updated forecasts. If the original plan is changed every time a problem arises, the reference needed to understand how the project is progressing is lost. Approved changes can be incorporated into a revised control version, but it is useful to retain the initial budget and schedule, as well as the reason and date for each modification.

Measure actual progress and relate it to expenditure

The percentage of progress should reflect work performed and verified, not merely time elapsed, materials ordered, or amounts invoiced. Depending on the cost item, progress can be measured through quantities completed, milestones achieved, or acceptance criteria defined in advance. The site manager or technical team validates the measurement; administration or the technical office records and assigns costs to the corresponding cost items.

The Earned Value Management (EVM) method compares three quantities, expressed in monetary terms:

• Planned Value (PV): the budget for the work that should have been completed by the cutoff date.
• Earned Value (EV): the budget corresponding to the work that has actually been completed.
• Actual Cost (AC): the cost incurred by that date to perform the work, even if the invoice has not yet been paid.

For example, if a cost item has a budget of 100,000 euros and 40% has been completed and validated, its earned value is 40,000 euros. If the cost incurred to achieve that progress is 48,000 euros, cost performance is worse than planned. The example is comparable only if the percentage completed and the cost are assigned to the same scope.

Use indicators as signals, not verdicts

Two basic ratios provide an initial reading:

• Cost Performance Index (CPI): EV ÷ AC. A result below 1 indicates that, for the work completed, more cost has been incurred than the budget allowed for; a result above 1 indicates less.
• Schedule Performance Index (SPI): EV ÷ PV. A result below 1 means that less work has been completed than planned by the cutoff date; a result above 1 means more.

Variances can also be calculated: EV − AC for cost and EV − PV for progress against the plan. In both cases, a negative difference indicates performance below plan in that dimension. EVM schedule variance is expressed in budgeted value, not directly in days of delay; it should therefore be read alongside the schedule and the sequence of activities.

These indicators do not, on their own, explain why a variance has arisen or guarantee the final cost. A low CPI may be due, among other possible causes, to lower-than-planned productivity, waste, rework, or incorrect cost allocation. Measurements, scope, and records must be checked before assigning a cause.

Monitor commitments, purchases, and subcontractors

Actual cost may lag behind obligations the company has already assumed. For this reason, in addition to recording costs incurred, it is advisable to review committed cost: purchase orders issued, contracts, and formal agreements that have not yet been fully reflected in invoices or recorded costs.

Comparing the budget, commitments, and actual cost by cost item helps identify cost pressures before they fully materialize. The team can review pending orders, prices, quantities, subcontractor payment applications, and scope changes, and update a forecast of final cost. This forecast should distinguish between costs already incurred, costs committed, and the cost still expected to complete the work; it should not be confused with the original budget.

Indirect costs—such as certain technical-office expenses, general services, or insurance—should also be included in monitoring using a consistent allocation method. Otherwise, a cost item may appear to be within budget while some of the cost is left out of the comparison.

Review changes before updating the forecast

Each change should be documented with its scope, reason, cost, and expected schedule effect, as well as its approval status. It is advisable to separate authorized modifications from requests that are still pending: mixing the two can distort the view of the current budget. If a change alters the baseline, the record should show what was modified and from when, without deleting the previous reference.

Reviewing changes also makes it possible to check whether a variance results from performing the work as planned or from a change in scope. This distinction matters when explaining the result and preventing the same problem from appearing several times under different categories.

Turn monitoring into decisions

The frequency of controls depends on the pace and complexity of the project, but it should be set in advance and maintained. At each review, the team can follow a simple cycle:

1. Close the data: set a cutoff date and validate physical progress, costs, purchases, and commitments.
2. Compare against the plan: review differences by cost item and the cost and schedule indicators.
3. Investigate the cause: distinguish between scope changes, recording errors, productivity, supplies, coordination, and other verifiable factors.
4. Update the forecast: estimate the expected effect on final cost and milestones, stating the assumptions used.
5. Assign a response: agree on an action, a person responsible, and a review date; then check whether the measure has worked.

Depending on the cause, the response may involve adjusting the sequence of work, reallocating resources, reviewing an order, or resolving an interference. A measure should not be considered effective merely because it has been agreed upon: its effect must be verified at the next control, and any impact on quality, scope, or safety must be recorded.

Earned value provides a quantitative structure for comparing progress and cost, but it depends on timely data, consistent measurement criteria, and correct allocation. It does not replace site inspection or technical judgment: it helps identify where to investigate and supports documented decisions, but it does not automatically explain every variance.