Earned Schedule (ES) Calculator
The time-based extension of EVM — more accurate than SPI alone for predicting when a project will actually finish.
Example: A project 6 months into a 12-month plan with an SPI of 0.85 (based on cost) might actually be tracking closer to month 4.5 of progress by the Earned Schedule method — a 1.5-month schedule slip that traditional SPI alone tends to understate as a project nears completion.
Earned Schedule method, developed by Walt Lipke (2003), extends EVM's cost-based SPI into a time-based metric.
How Earned Schedule is calculated
Earned Schedule (ES) finds the point on your cumulative Planned Value curve where the curve's value equals your actual Earned Value, then interpolates linearly within that month to get a fractional time. SV(t) and SPI(t) then compare that earned TIME against the actual time elapsed (AT) — a genuinely time-based measure, unlike the cost-ratio SPI from standard EVM. IEAC(t) projects the total duration forward at the current SPI(t) trend.
Earned Schedule is designed to sit alongside, not replace, standard cost-based EVM metrics — see the Earned Value Management calculator for CPI, standard SPI, and EAC. If your planned value curve itself is built from uncertain activity durations, the PERT Estimating calculator can help produce three-point duration estimates to feed into your schedule before tracking begins.
Frequently asked questions
- Why not just use SPI to predict the completion date?
- SPI is a cost-based ratio (EV/PV) that mathematically converges to 1.0 near the end of a project regardless of true schedule health, making it unreliable for late-stage forecasting. Earned Schedule interpolates actual TIME progress from your PV curve instead, so SPI(t) stays meaningful all the way to completion.
- How do I fill in the PV S-curve without a full project plan?
- Use "Generate a typical S-curve" — enter your planned duration and total budget (the cumulative PV at completion) and it fills in a standard slow-start / fast-middle / slow-finish curve you can then fine-tune month by month.
- What happens if my earned value is ahead of the whole curve?
- Earned Schedule extrapolates beyond the planned duration using the final segment's rate, so an ahead-of-plan project correctly shows an ES beyond your planned duration rather than being capped at it.
- What is Earned Schedule (ES)?
- Earned Schedule is a time-based extension of standard Earned Value Management. Rather than measuring schedule performance in dollars (as traditional SV and SPI do), it finds the point on your planned value curve corresponding to your current earned value, expressed in units of time — giving a genuinely time-based schedule health metric.
- How does ES differ from standard EVM?
- Standard EVM measures schedule variance as EV − PV, in cost units — which mathematically converges to zero (and SPI to 1.0) as a project nears completion regardless of whether it's actually on time. Earned Schedule instead interpolates real elapsed time from the planned value curve, so its metrics remain meaningful all the way through to project completion.
- What is SPI(t) and what does it tell you?
- SPI(t) is the time-based Schedule Performance Index — Earned Schedule divided by Actual Time. A value above 1.0 means the project is progressing faster than planned in time terms; below 1.0 means it's falling behind schedule, even late in the project when the standard cost-based SPI would be unreliable.
- When is ES more useful than standard EVM metrics?
- ES is most valuable in the second half of a project, precisely when standard SPI becomes unreliable due to its convergence toward 1.0. It's also useful whenever you need a real predicted completion date rather than just a cost-based performance ratio.
- What is IEAC(t)?
- IEAC(t) (Independent Estimate at Completion, time-based) projects the total project duration forward based on the current SPI(t) trend — essentially answering "if this schedule performance trend continues, when will the project actually finish?"