The data date is the "as of" date the schedule is being calculated from — the line that separates what's already happened from what's still being forecast. Drag the slider below and watch what it does to a six-activity programme.
What the data date is
Every P6 schedule carries one data date — the single date the whole forward pass is anchored to for anything not yet complete. Activities that have finished are locked to their actual dates; activities still in progress or not started are recalculated forward from the data date, not from the project's original start.
How P6 uses it in the forward pass
For an in-progress or not-started activity, P6's forward pass uses the later of the data date or the activity's logic-driven early start as the effective start for remaining work. That's why moving the data date forward without also updating progress can silently push every incomplete activity's dates forward with it, whether or not real progress happened.
What happens when it's wrong
A data date left behind reality (not advanced to match the actual reporting period) makes P6 think less progress exists than actually does, understating how far along the project is. A data date pushed ahead of where progress has actually been recorded does the opposite — it can make incomplete work look on track when it isn't, or worse, let the engine calculate dates for activities as if unfinished predecessors were done.
Retained logic vs progress override
These are the two ways P6 can treat an out-of-sequence activity — one that's progressing before its logical predecessor has actually finished. Retained logic respects the original relationship: a successor can't be scheduled to proceed until its predecessor is complete, even if that means showing a gap. Progress override lets the successor's actual progress stand as reported, effectively ignoring the unfinished predecessor relationship for scheduling purposes. Retained logic is the more conservative, defensible default for almost all construction schedules; progress override can mask a genuine sequencing problem.
Data date vs report date vs update date
These three are easy to conflate. The data date is the date the calculation is anchored to inside P6. The report date is whatever date appears on the printed or exported report, which may not match the data date if the report was generated later. The update date is when the underlying progress data was actually collected on site, which may be earlier than both if there's a lag between site data collection and schedule update.
The most common mistake
Leaving the data date at the project start date and never advancing it. Every subsequent update then recalculates the entire schedule as if no time has passed and no progress has occurred — the single most common way a "live" P6 schedule quietly turns back into a static baseline that no longer means anything.