Schedule Slippage: Spot It Early, Then Recover the Date

A schedule rarely slips by a month. It slips by two days at the status meeting, three more the week after, and a week once someone finally re-forecasts the finish. Each update is small enough to explain away, and by the time the milestone is missed, the cheap ways to recover it are gone.

The direct answer: schedule slippage is the gap between when work was baselined to finish and when it is now forecast to finish, counted in working days. You catch it early by reading three signals before any milestone is missed: late starts, shrinking float on the paths next to the critical path, and percent complete that stops moving. It is common: only 36 percent of organizations mostly or always complete projects on time, according to Wellingtone's State of Project Management report, published in March 2026.

In short. Slippage is forecast finish minus baseline finish. It announces itself weeks ahead, in late starts, eaten float and stalled progress, so read those at every status date. When it shows, recover in order of cost: re-sequence, add resource to critical tasks, fast-track, crash, and only then move the date, openly.

How do you measure schedule slippage?

You need a baseline first. Without a saved copy of the agreed dates, every slip can be argued; with one, it is a number. The baselines and schedule variance features are built for exactly this comparison, and the table below sets out the measures worth reading at each status date.

Finish variance in days and schedule variance in earned value can disagree on the same project, because one counts dates and the other counts the value of the work done. Schedule variance, the EVM formula and the baseline version works through both on one example.

What are the early warning signs of slippage?

Take a release baselined to finish on working day 60. At the status date on day 30, nothing is late yet on the milestone report, but three things are already true:

1. A late start. Design review was planned to start on day 18 and started on day 22. It sits on a path that had 7 days of total float and now has 3.
2. Stalled progress. The build task is 40 percent complete after three weeks of a five-week duration, the same figure it reported last week.
3. A falling BEI. Eighteen tasks were baselined to finish by day 30 and fifteen have, so the BEI is 15 / 18 = 0.83.

Roll those forward and the forecast finish is day 64: four days of slippage that no milestone has reported yet. The diagram below shows how the slack on a near-critical path is used up before the finish moves at all.

Total float is the number to watch on those paths, because a path next to the critical path becomes the critical path the day its float runs out. Total float vs free float explains which of the two to read.

How do you recover a slipping schedule?

Recover in order of cost, cheapest first, and only on the tasks that drive the finish. Shortening a task with float buys nothing.

1. Re-sequence. Check the logic on the critical path. Links that only reflect a preference, not a real dependency, can be removed so work runs side by side with the same people.
2. Add resource to critical tasks. Move people from tasks with float to tasks without it. Someone new to a task usually slows it before they speed it up, so do this early, not in the last week.
3. Fast-track. Overlap tasks planned in sequence, such as starting tests on finished modules while the rest are built. The cost is rework when the earlier task changes.
4. Crash. Pay to shorten critical tasks with overtime or extra contractors, starting with the task that is cheapest per day saved. Crashing vs fast-tracking has the arithmetic.
5. Move the date and say so. If none of the above closes the gap, re-forecast the finish and tell the sponsor in the same week. Keep the original baseline so the slip stays measurable, and save a new one only once the new date is agreed.

How do you track slippage in Onplana?

Baselines are on every Onplana plan, Free included. The Baseline view under a project's Plan tab reads the drift against a saved baseline in dates and duration, and the Gantt can overlay the baseline bars beside the current ones (capture and compare baselines). The critical path and float show on the same Gantt.

For the early signals, the Schedule Quality view runs all fourteen checks of the DCMA 14-point schedule assessment on every plan, including the critical path length index and the baseline execution index, and lists the tasks behind each result (check a schedule against the DCMA 14-point assessment).

If the schedule is a file rather than a project, start with the free Schedule Health Check, which reads an .mpp or Microsoft Project XML file of up to 20 MB and reports missing logic, unrealistic durations and deadline risks before you trust the dates. To keep working the file on your own computer, Onplana Schedule is a free Windows and Mac app that shows the critical path and float. Microsoft Project XML is read on your machine and nothing is uploaded; every other format, an .mpp included, is converted on Onplana's servers, and the uploaded copy is deleted within 3 days and removed from backups 7 days after that. Publish, in the app, creates the project in Onplana when the plan needs a team.

Find the slippage signals in a schedule you already have Upload a project file to the free Schedule Health Check and see missing links, unrealistic durations and deadline risks before the next status date. No signup required. → Open the Schedule Health Check

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