Actual Cost (AC)
Actual Cost (AC) is the total cost actually incurred for the work performed to date - on a labour-led package, the real hours booked (priced at real rates) plus materials. Also called the Actual Cost of Work Performed (ACWP).
Actual Cost is the only EVM input that comes from reality rather than the plan: the hours genuinely worked and the money genuinely spent on the work completed so far. Set against Earned Value it yields the cost metrics - Cost Variance (CV = EV - AC) and the Cost Performance Index (CPI = EV / AC).
The classic failure mode is an AC that lags the work: timesheets reconciled weeks later, agency labour invoiced monthly, materials booked when invoiced rather than when consumed. Every day of lag flatters CPI and delays the moment an overrun becomes visible.
The discipline that matters is matching scope: AC must cover exactly the work EV claims - same activities, same period. In WBSync, AC accrues per WBS node from approved labour entries (unapproved hours never touch the KPIs) plus imported material costs, so the CPI a QS reports is built on checked data.
Want this calculated live across your whole project? Start free with WBSync — 30-day trial, up to 30 active operatives, no card required.