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Construction cost overrun calculator

Find out where a job will finish while there is still time to change it. Enter the budget, what has been spent and how far along the work really is — the calculator forecasts cost at completion from the job’s own performance and from its recent burn, and tells you when the two disagree.

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Tool 01

Cost overrun & forecast at completion

Enter the budget, what you have spent and how far along the work is. You get the forecast two ways — performance-based and burn-based — and the verdict tells you when the two disagree, because that is usually the first sign of an overrun.

Job inputs

Result

Earned value = BAC × % complete. CPI = EV ÷ AC (below 1 means you are paying more than the work is worth). EAC (performance) = BAC ÷ CPI. EAC (burn) = AC + (spend ÷ 3) × months remaining. VAC = BAC − EAC. TCPI = what the remaining work must achieve to still land on budget — above 1.1 is usually not going to happen. Months to exhaustion = (BAC − AC) ÷ monthly burn.

How to use it

  1. Enter the budget at completion — the job’s total cost budget.
  2. Enter cost to date from the job cost ledger.
  3. Enter work complete from the schedule or installed quantities — not from cost.
  4. Optionally add the last three months’ spend and the months remaining for the burn forecast.

A worked example

A $4.0M-budget job has spent $1.8M and is 38% complete. Earned value is $1.52M, so CPI is 0.84 — each dollar is buying 84 cents of planned work — and the performance forecast is $4.74M, about $740K over. But the last three months’ burn ($420K) carried forward says $3.06M. When the two disagree by more than 10% of budget the calculator flags it: either the 38% is optimistic or the recent burn is not representative. To land on budget, the remaining work would need a TCPI of 1.13.
Want the background? The guide works through the arithmetic, the mistakes that hide problems, and a checklist.
Read: Job cost forecasting →

Questions

How do you calculate a construction cost overrun?

Forecast cost at completion (EAC) and subtract the budget. The usual EAC is budget ÷ CPI, where CPI is earned value (budget × % complete) divided by actual cost.

What is a good CPI on a construction job?

1.0 or above means the work is costing what it was budgeted to cost or less. Between 0.95 and 1.0 deserves watching; below 0.95 is usually a real overrun.

What does TCPI tell me?

The cost performance the remaining work must achieve to finish on budget: (BAC − EV) ÷ (BAC − AC). A TCPI well above the CPI you are running means the budget is no longer realistic.

Why are there two forecasts?

The performance forecast carries the job’s cost efficiency forward; the burn forecast carries its recent spending rate forward. When they disagree by more than 10% of budget, percent complete or the recent burn is usually wrong.

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Want this on your live data, every morning?

These tools are manual. The dashboard does the same arithmetic across every job, every company and every week — plus the money-at-risk view, the audit findings and the overrun radar. Join the private beta and we will connect it to the systems you already run.