Forecasting Remaining Effort: How EAC (Estimate at Completion) Works
Midway through a project, can you answer "if we keep going at this pace, how many hours will it take in total?"
"Design is done and we've already burned 40% of the budget. Will the remaining stages really fit in the other 60%?" Whether you can answer that question with a number rather than a feeling has a big impact on the quality of your project management.
EAC (Estimate at Completion) is the concept built to answer it. It sounds technical, but the idea is simple. This article covers the basics of EAC and how to use it in practice.
What is EAC?
EAC is an estimate of "if we keep progressing at the current actual pace, what will the total effort be at project completion?"
Say you have a project planned at 100 hours. At the point where 40% of the work is done, your actual hours are 50.
You can now see the fact: "the plan said 40% would take 40 hours, but it actually took 50."
If the remaining 60% proceeds at the same pace, the total at completion can be estimated as:
EAC = actual hours ÷ progress rate = 50 ÷ 0.4 = 125 hours
The original estimate was 100 hours, but at the current pace it will be 125. If this number appears mid-project, there's still time to act on it.
How EAC differs from a gut-feel forecast
You can certainly have the feeling "this is heading somewhere bad." But feelings aren't reproducible, and you can't hand them to someone else.
EAC is useful because the forecast — "how many hours over we might end up" — comes out as a number.
- The feeling: "the design phase is slower than expected"
- vs. the number: "computed from the design phase's pace, the project EAC is 150 hours — 50 over the original estimate"
With the latter, you can take next actions: explain to the client, revisit scope, negotiate additional hours. Stay at the feeling stage and "it'll probably work out somehow" procrastination creeps in.
Using EAC as an early-warning system
In practice, the most effective approach is to compute EAC at the end of every phase.
When the requirements phase ends, calculate "actual hours ÷ progress rate." If EAC already far exceeds the original estimate, you can decide early: "the design phase onward needs revisiting."
Conversely, if EAC comes in under the estimate, you can also conclude "we're ahead of plan — the later phases have slack."
Building a cycle of computing EAC at every phase boundary turns the late-project discovery of "we're out of budget" into a mid-project forecast of "at this pace, we will run out of budget."
What you need to compute EAC
Two pieces of information are required.
1. Actual hours (how long things have taken so far)
You need time tracked at the task level and aggregated per phase. Not just "how many hours total so far," but a structure that can answer "how many hours went into the design phase."
2. Progress rate (how much of the whole is done)
Measuring progress is the tricky part. "Completed tasks ÷ total tasks" is common, but unless tasks are uniform in size the rate won't be accurate.
A practical alternative is to use "how much of the estimated effort has been consumed (consumption rate)" in place of progress. For example: "20 actual hours against the design phase's 30-hour estimate → the design phase is 67% consumed."
A quick EAC using per-phase consumption rates
When an accurate "progress rate" is hard to produce, simply checking per-phase consumption — "is this phase going to fit its budget?" — is already quite practical.
For example:
- Design phase estimate: 30 hours
- Design phase actuals (at phase end): 42 hours (140%)
If design took 140% of its estimate, and the same trend continues through the remaining phases, the whole project can be forecast at 140%:
- Original estimate: 100 hours
- EAC (rough): 100 hours × 1.4 = 140 hours
With "a 40-hour overrun is forecast" in hand, you can move early on client communication and estimate revisions.
Using EAC to improve accuracy
EAC is useful as an in-flight management tool, but it also has value after the project ends.
At project close, compare three numbers: the original estimate, the EAC values you computed along the way (the completion forecasts at each phase end), and the actual final effort.
- How close were the EAC values to the actual final effort? → evaluates the accuracy of your EAC calculations
- How far did the original estimate diverge from the EAC values? → identifies which phases were underestimated
Repeat this retrospective and you'll see "in which phases my EAC tends to drift the most." That becomes calibration material for your next project's estimate.
Summary
- EAC (Estimate at Completion) estimates "at the current pace, how many hours will the project take in total"
- The formula: actual hours ÷ progress rate (forecasts based on estimate consumption rates also work)
- Checking EAC at every phase end enables early warning in mid-project
- Turning "a vague worry" into "a numeric forecast" makes the next action easier to take
- Comparing EAC values with actuals after the project reveals your estimation tendencies
EAC may have the image of "heavyweight project management methodology," but the idea itself is simple. As long as you have per-phase effort records, it's a concept you can use even on small engagements.
The "EAC (Estimate at Completion) forecasting" covered in this article is exactly what LayerClock supports. Per-phase actuals are aggregated automatically, with a real-time completion forecast based on your current pace (Business plan). Set up your recording habits on the free plan first, then give it a try.