Why is estimated cost almost never equal to actual cost?

The estimate rests on assumptions (rates, quantities, norms) that change in practice

Estimates are deliberately made wrong

Actual cost is calculated before the work

Contingency makes the two always equal

Which is an example of a quantity change?

Rock found during excavation instead of ordinary soil

What is the purpose of the usual 3 to 5% contingency?

To cover uncertainty, though exact equality is still not expected

To guarantee that actual cost equals the estimate

To replace the need for revised estimates

2080 Bhadra · 3 marks

Estimated cost is never the actual cost

Short answer

Estimated cost is a forecast that almost never matches actual cost because material prices, labour wages and site conditions change, quantities may vary due to design alterations or unforeseen ground, and actual productivity and wastage differ from standard norms. Contingency is added to cover such uncertainties.

Estimated cost is never equal to the actual cost of a project. Give your opinion.

I agree. The estimated cost is a forecast made before the work, from drawings and current rates. The actual cost is what is really spent when the work is finished. The two are almost never equal because an estimate rests on assumptions that change in practice.

Reasons:

Change in rates: prices of cement, steel, fuel and wages rise or fall between the estimate and construction (price escalation).
Quantity changes: design variations and site conditions (for example rock found in excavation, or a different soil) change the quantities actually executed.
Norms and allowances: estimates use standard norms and wastage allowances, but real wastage and productivity differ.
Unforeseen events: floods, landslides, strikes, delays, shortage of materials, or the need for extra safeguards.
Variation orders and additional work requested by the owner.
Human and approximation errors in taking out quantities, and omitted items.

Estimates carry a contingency (usually 3 to 5%) for such uncertainty. A careful estimate can come close to the actual cost, but exact equality is a matter of chance. When the difference becomes large, a revised or supplementary estimate is prepared to keep the cost under control.

✓ Answer checked by Claude Opus 5.5 (high effort)

Estimated cost never actual; data required · Estimating and Costing, chapter 1
Purposes of estimating; estimate never actual cost · Estimating and Costing, chapter 1
Compare estimated cost and actual cost · Estimating and Costing, chapter 1
Estimate, quantity survey, estimated vs actual · Estimating and Costing, chapter 1
Cost variance analysis from standard and actual · Engineering Economics, chapter 1

All Estimating and Costing chapter 1 questions →

Estimated cost is never the actual cost

Related questions