Trending & Forecasting of CPM Schedules

Trending vs. forecasting

The CPM gives you a forecast finish each period — but it assumes all remaining work goes to plan from the data date forward. Trending challenges that assumption: if you've slipped a bit every month for four months, the honest forecast isn't "on time from here" — it's "more slip is coming." Trending turns the history of updates into a leading indicator.

Metrics worth trending

Several schedule signals, tracked update-over-update, reveal where the project is heading:

1. Forecast completion date — plot the projected finish at each update. A steadily slipping line is the clearest early warning of trouble.
2. Float trend — total float on key paths eroding period after period signals the schedule is tightening toward criticality.
3. Progress / productivity rate — actual progress vs planned (an S-curve gap, or hours-per-unit) — a falling rate forecasts a later finish.
4. Critical-path stability — a critical path that jumps around each update, or grows longer, signals an unstable, deteriorating plan.

From trend to forecast

Forecasting takes the measured trend and extends it. The simplest, most powerful idea: if work is being delivered at a rate different from plan, the remaining work will likely continue at a similar rate — so the finish moves accordingly. A crew running at 75% of planned productivity won't suddenly hit 100%; the honest forecast assumes the trend continues unless something changes.

Simple performance forecast

Ten things to remember

1. Trending tracks metrics across updates; forecasting projects them forward.
2. One update is a dot; the series is a direction — the trend is the leading indicator.
3. The CPM date assumes plan-from-here — the trend challenges that assumption.
4. Trend the forecast finish, float, productivity, and critical-path stability.
5. S-curves make the gap visible — actual below planned and widening = late and getting later.
6. If performance ≠ plan, assume it continues unless something concrete changes.
7. Beware the optimistic "make it up later" forecast with no recovery plan.
8. Don't call a trend from one data point — but don't ignore a sustained one either.
9. Forecasting buys time to react — early honesty beats late accuracy.
10. A simple factor is an indicator, not a replacement for re-statusing and recalculating the CPM.