How do I spot a cost blowout on a construction project early?
Watch the signals that move before the cost report does: forecast cost to complete against budget, variations agreed on site but not yet priced, costs committed in orders but not yet invoiced, and programme slippage that will add preliminaries. Review them weekly. By the time a blowout shows in the monthly cost report, most of it is already spent.
Why the cost report is late
Accounting records what has been invoiced. A lot of cost is committed well before the invoice arrives: orders placed, labour booked, variations agreed with a handshake. The cost report catches up weeks later.
Four early signals
Cost to complete: the PM's forecast of what's left, compared with budget remaining.
Unpriced variations: work agreed but not yet priced or approved.
Committed costs: orders and subcontracts not yet invoiced.
Time: every week of delay adds site costs, even if nothing else changes.
Look weekly
A weekly cost status, red, amber or green, catches drift while there's still time to recover it through pricing variations, resequencing work or a conversation with the client.
Make it automatic
These numbers live in your accounting and project systems. Pulling them together automatically means the warning shows up without someone having to build a spreadsheet.
Common questions
What's the most common early sign?
Variations that have been done but not priced. They quietly eat margin until someone notices.
Who should own cost to complete?
The project manager, reviewed by whoever is responsible for the commercial result.
How often should cost be reviewed?
Weekly for status, monthly for the full report.
Can software predict a blowout?
It can flag the trend early from your own data. People still decide what to do about it.