Earned Schedule Calculator
Calculate Earned Schedule (ES) and the time-based Schedule Performance Index SPI(t) = ES / AT.
SPI(t) = ES / ATInterpretation Guide
- SPI(t) ≥ 1On or ahead of planned time.
- 0.9 – 1.0Mild slip in time.
- < 0.9Material time slip.
Example
ES = 18 weeks, AT = 20 weeks → SPI(t) = 0.90 (10% behind in time).
Real-world use cases
- Late-phase forecasting where SPI ≈ 1 misleads
- Long-duration construction programmes
Common mistakes
- Confusing ES with EV — ES is measured in time units
Professional tips
- Use SPI(t) instead of SPI for projects past 70% completion
Frequently asked questions
Why use Earned Schedule?
Standard SPI naturally trends to 1.0 near project end even on late projects. ES corrects this by measuring schedule in time, not cost.
What this tool does
Calculate Earned Schedule (ES) and the time-based Schedule Performance Index SPI(t) = ES / AT.
It applies the standard formula SPI(t) = ES / AT so planners, schedulers and PMOs get a defensible number they can put in front of a steering committee.
Looking for the underlying terminology? Open the PM Glossary or the PM Cheat Sheet for quick references on EVM, scheduling and risk terms.
When to use it
- Late-phase forecasting where SPI ≈ 1 misleads
- Long-duration construction programmes
Typical owners: project managers, planning engineers, project controls leads and PMO analysts running weekly or monthly performance reviews on EPC, infrastructure, IT and construction projects.
How to interpret the result
Treat the number as a signal, not a verdict. Read it together with the trend over the last 3–6 reporting periods, the critical-path status, and the risk register before you change the plan.
- Compare against the baseline, not against another project.
- Investigate the drivers behind the value before reporting it up.
- Pair it with at least one complementary KPI (cost, schedule, risk or quality).
Worked example
ES = 18 weeks, AT = 20 weeks → SPI(t) = 0.90 (10% behind in time).
In a real project review, document the inputs, the resulting value, the interpretation, and the corrective action you committed to. That audit trail is what turns a calculator output into a controls decision.
In-depth guide: Earned Schedule Calculator
Earned Schedule (ES) is the time-based extension of EVM developed by Walt Lipke in 2003 to fix the well-known late-phase failure of the standard SPI. Standard SPI is computed in dollars and mathematically converges on 1.0 as a project approaches completion — even on a project that is six months late, SPI = 1.00 the day the last dollar of EV equals the last dollar of PV. That is useless for late-stage forecasting.
Earned Schedule fixes this by projecting EV onto the time axis of the planned-value curve. ES is the point in time at which the current EV should have been earned according to the baseline. SPI(t) = ES / AT (actual time) is then a true time-based efficiency: it stays meaningful right through to project close-out.
Earned Schedule is now the de-facto standard for late-phase forecasting on long-duration programmes and is referenced in PMI's Practice Standard for Earned Value Management, AACE RP 11R-88, and ISO 21508. Most enterprise project controls platforms — including Primavera P6 EPPM with the EVM module, Deltek Cobra, and ARES PRISM — compute SPI(t) natively.
When to use it (and when not to)
Use SPI(t) from project start as a parallel metric to SPI, and as the primary schedule efficiency metric after ~60–70% completion. It is also the right metric for long-duration construction programmes, multi-year IT transformations, and any project where the dollar SPI is being distorted by front- or back-loaded planned value.
Do not use SPI(t) on very short projects (under ~8 reporting periods) where the time-translation arithmetic is too coarse to be useful. Stick with standard SPI in that case.
Related KPIs to read alongside
Pair SPI(t) with standard SPI (for cross-validation in mid-project), SV(t) = ES − AT (the time-based schedule variance), critical-path total float, and the count of activities with negative float. For forecasting use the Time-based Estimate at Completion: IEAC(t) = AT + (PD − ES) / SPI(t), where PD is the planned duration.
Worked example — desalination plant commissioning
A desalination plant has a 100-week baseline. At AT = 80 weeks, the team has earned $42M of EV out of a $50M BAC. Looking at the baseline PV curve, $42M was supposed to have been earned at week 72 — so ES = 72 weeks.
SPI(t) = 72 / 80 = 0.90. The standard SPI for the same data date is 42 / 45 = 0.93 (because PV at week 80 is $45M, not the full $50M). The two metrics tell a slightly different story — SPI(t) is more pessimistic and, on a project this far through, more accurate.
Translating to a forecast finish date: at SPI(t) = 0.90, the remaining 20 baseline weeks will take 20 / 0.90 ≈ 22 weeks, so the project finishes around week 102 — a 2-week slip against the 100-week baseline. The standard SPI would have implied a smaller slip and given the steering committee false comfort.
Decision table
| Signal | What it means | Recommended action |
|---|---|---|
| SPI(t) ≥ 1.00 | On or ahead of plan in time. | Hold; cross-check against critical-path total float. |
| 0.95 ≤ SPI(t) < 1.00 | Mild time slip. | Note in PMO log; trend over next 2 periods. |
| 0.90 ≤ SPI(t) < 0.95 | Material time slip. | Root-cause analysis; revise forecast finish date. |
| SPI(t) < 0.90 | Significant time slip. | Formal recovery plan; consider rebaseline of the schedule. |
Common pitfalls in the field
- Computing ES from a non-cost-loaded schedule. ES requires a baseline PV curve, which requires the schedule to be cost-loaded. On schedules that are not cost-loaded, use duration-weighted progress instead and label the metric as a proxy, not true Earned Schedule.
- Confusing ES with EV. They are different quantities — EV is in dollars, ES is in time units. The two are linked through the baseline PV curve but are not interchangeable.
- Using SPI(t) as a substitute for critical-path analysis. SPI(t) is an aggregate efficiency metric; it does not tell you which activities are slipping. Always read it alongside the longest-path report and the float-erosion trend.
Featured in Academy articles
This calculator is referenced in the FAQs of these Academy articles — read them to understand the theory behind the numbers.
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