Glossary
Earned Value vs Earned Schedule
Earned Value (EV) measures schedule performance in cost units and converges to zero at project end. Earned Schedule (ES) measures schedule performance in time units and stays meaningful through the entire project lifecycle.
Earned Value (classical) vs Earned Schedule — schedule metrics compared.
| Earned Value (EV) | Earned Schedule (ES) | |
|---|---|---|
| Unit of measure | Cost (£, $) | Time (days, weeks, months) |
| Headline schedule metrics | SV = EV − PV; SPI = EV ÷ PV | SV(t) = ES − AT; SPI(t) = ES ÷ AT |
| Behaviour at project end | Converges to 0 / 1.0 even on late projects (the convergence problem) | Stays meaningful — reflects actual schedule performance through closeout |
| Best for | Mid-project cost-schedule integration; baseline-vs-actual cost performance | Schedule forecasting late in the lifecycle; honest closeout metrics |
| Reference framework | AACE 11R-88; PMI EVM Standard | AACE 64R-11; Lipke (2003) Earned Schedule |
| Tool support | All EVMS tools natively (Deltek, Cobra, Acumen, Ecosys) | Same tools — usually a configurable report; some need custom calc |
| Typical UK use | Default schedule metric on NEC4 and MoD EVMS contracts | Increasingly required as supplementary metric on Major Projects with MPRP/IPA scrutiny |
Earned Value Management produces two schedule metrics: Schedule Variance (SV = EV − PV) and the Schedule Performance Index (SPI = EV ÷ PV). Both express schedule performance in cost units. Earned Schedule (ES), introduced by Walt Lipke in 2003, converts schedule performance back into time by asking a different question — "at what point in the planned schedule should we have earned the value we've earned so far?" — and produces a parallel set of metrics in time units: SV(t) and SPI(t).
The reason this matters is a well-known limitation of classical EVM. SPI and SV always converge to 1.0 and 0 respectively at project completion, regardless of whether the project finished early, on time, or six months late, because EV and PV both equal BAC at completion. A project that is six months late will, in its final report, show SPI = 1.0 — a blatantly wrong reading of schedule performance. Earned Schedule's SPI(t) does not have this convergence problem; it remains a faithful measure of schedule efficiency through the closeout phase.
For UK infrastructure programmes that report monthly through the late stages of delivery, SPI(t) is the more honest metric. Most modern EVMS implementations now produce both — Earned Value figures for traditional cost-schedule integration, Earned Schedule figures for forward-looking schedule forecasting. AACE Recommended Practice 64R-11 covers both. Practitioners working on programmes where schedule completion is governance-critical (NEC4, MoD MPRP, IPA gateway) should be comfortable reading and producing both sets of metrics.
Used in practice
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Frequently asked
- What is the difference between Earned Value and Earned Schedule?
- Earned Value Management measures schedule performance in cost units (SV = EV − PV, SPI = EV ÷ PV). Earned Schedule converts these into time units (SV(t), SPI(t)) by asking when you should have earned the value you have earned. The practical difference is that classical EV's schedule metrics converge to zero/1.0 at project completion even on late projects, while Earned Schedule's time-based metrics remain meaningful through closeout.
- Why does SPI become unreliable late in a project?
- SPI = EV ÷ PV. As a project approaches completion, both EV and PV approach the Budget at Completion (BAC) — eventually they're equal, and SPI = 1.0 regardless of how late the project actually finished. This means a project six months overdue can report SPI = 1.0 in its final month. Earned Schedule's SPI(t) doesn't suffer from this — it expresses schedule performance in actual time units, so a six-month overrun shows as SPI(t) ≈ 0.85 even at closeout.
- Should we use Earned Value or Earned Schedule on a UK infrastructure programme?
- Both. Earned Value is the contractual / EVMS-mandated framework on NEC4 and MoD contracts and remains the default for cost-schedule integration. Earned Schedule is supplementary — most useful for forward-looking schedule forecasting, especially in the back half of the programme when SPI is no longer reliable. Many modern EVMS implementations produce both; reporting both keeps the client honest.
- Who developed Earned Schedule?
- Walt Lipke, who introduced the framework in a 2003 paper while at Tinker Air Force Base. The methodology has since been formalised in AACE International Recommended Practice 64R-11 ("CPM Schedule Risk Modelling and Analysis") and is now standard supplementary practice on major US DoD and UK MoD programmes.
Related terms
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