Creating dependencies, with lag and lead time

Linking two tasks

Dependencies are a property. Add it from the + at the end of the header row, under Schedule & PMO, and every task gets a Dependencies cell showing what it waits on. Click the cell, or open the task, and use the "Depends on" section to pick the tasks it waits for. A task can depend on any number of others.

Templates that ship with linked tasks add the property for you. A project that has not added it shows the Impact Matrix as a one-click prompt to add it, since the matrix reads those links.

Dependencies are Finish-to-Start: the dependent task starts after the task it depends on finishes. This is the link type that describes most real sequencing -- you cannot test what has not been built.

Lag and lead time

Each dependency carries a lag in days. A lag of 5 means the dependent task starts five days after its predecessor finishes, which is how you model a wait that is real but is not work: hardware shipping, a client review window, concrete curing.

A negative lag is lead time -- the dependent task starts before its predecessor fully finishes. Set the lag to -3 to let a task begin three days early.

Lag is carried through the schedule calculation, so it affects propagated delays and float, not just where the bar is drawn.

Circular chains are blocked

If a set of dependencies would create a loop -- A waits on B, B waits on C, C waits on A -- the change is rejected with a message telling you to remove the loop. A circular chain has no valid schedule, so there is no sensible way to draw or calculate one.

If a loop ever arrives from an import or a direct write rather than through the editor, the views still render every task rather than silently dropping the ones caught in the loop.

What happens once tasks are linked

Linking tasks is what turns the rest of the analysis on. The Impact Matrix can only tell you what a task affects if something is linked to it, float is measured along the dependency network, and delay simulation propagates along those links.

This is the highest-value thing you can do to a project: a fully populated task list with no dependencies is a spreadsheet with nicer bars.