Earned Schedule (ES)
Earned Schedule (ES) translates Earned Value into time: the date by which the baseline planned to have earned what has actually been earned today. It yields time-based metrics - SPI(t) = ES / AT - that stay honest to the end of the project, where cost-based SPI goes blind.
Classic schedule metrics have a known flaw: because EV converges on PV as work completes, SPI drifts back to 1.0 and SV to zero on every project, however late it finishes. Earned Schedule fixes this by asking when, not how much: find the point on the baseline PV curve where planned value equals today's EV - that calendar point is the Earned Schedule.
Set ES against Actual Time (AT, the time actually elapsed) and the familiar arithmetic returns in time units: SPI(t) = ES / AT and SV(t) = ES - AT. If 8 months have elapsed but the baseline expected today's EV at month 6.5, SPI(t) is 0.81 and the work is running 1.5 months behind - a statement no cost-based SPI can make cleanly.
ES keeps discriminating between late and on-time right through project completion, and forecasting follows the same pattern as cost: estimated duration = planned duration / SPI(t). It complements rather than replaces critical-path analysis - ES sees the budget-weighted whole, the programme sees the logic links.
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