99 Tricks and Traps for Microsoft project

Elapsed Durations, Leads and Lags in MS Project

Elapsed Durations

If you assign a task an Elapsed duration, the task will ignore all calendars and will be scheduled 24 hours a day and 7 days per week. To enter an elapsed duration, type an “e” between the duration and units.

  • This is useful for tasks such as curing concrete or computer processes running 24 hours per day.
  • The Total Float will calculate approximately three times longer than a task on an 8-hour per day calendar (depending on the length of the lunch break) and this may be misleading.

The example below shows the difference between a 7-Elapsed Day task and a 7-day task on a Standard (5-day per week) calendar.

leads and lags in ms project

Float on Tasks with Elapsed Durations

The Float on Elapsed Duration tasks is calculated on a 24-hour per day calendar and will be different than a task on an 8-hour per day calendar:

float on tasks with duration in ms project

Elapsed Leads and Lags

An elapsed lead or lag may also be assigned to relationships and these also ignore all calendars:

elapsed leads and lags in ms project

% Lags

A Percentage Lag, or Negative Lag, increases the Lag duration as the predecessor duration increases:

task dependancy in ms project

duration slack in ms project

The lag duration is calculated on the successor calendar. When the successor task is changed from an 8-hour per day calendar to a 24-hour per day calendar, the elapsed duration of the successor is reduced, as well as the elapsed duration of the lag.  Now the Float is calculated on a 24-hour per day basis.

Things get a bit tricky here!

duration slack 2 in ms project

Note: Microsoft Project 2000 calculates the lag on the Project Calendar.

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