I'm not sure what combination of task dependency type and lead/lag duration to use for the following scenario.

  • Item B is a large, complicated assembly that includes a subcomponent called Item A
  • Development of Items A and B are tracked in separate tasks, have have durations of 2 and 9 months, respectively
  • Item A needs to be delivered within 5 months of starting work on the Item B

I’m looking for a way to have Task A and B start simultaneously, but create a task dependency so I can see that Task A has three months of slack until it begins to affect the delivery of Task B.

I tried making a FS dependency between Task A and Task B with a -5 emo lag, but that created a gap in Item B at the current date and moved the end date out 6 weeks.

  • If you habe a can and a need to requirement, why not focus on the stronger one and set both tasks to start as early as possible? During execution, you could update your plan with the real start dates.
    – Tob
    Commented Jun 14, 2015 at 4:18
  • Are the same resources involved in both of these activities? What is the lead time for delivery of Item A? What is the effort required to procure each of them?
    – Iain9688
    Commented Jun 14, 2015 at 12:38
  • @Tobias I don't understand your question. Upon rereading me question, perhaps it’s unclear that Item A is incorporated into Item B. I’ll update the question accordingly.
    – Adam Wuerl
    Commented Jun 15, 2015 at 5:03
  • @lain9688 No, the same resources aren't involved, although I’m not sure how that's relevant. The lead-time for A is a few months, but less than 5. The effort to procure is relatively minimal: a few hours to negotiate subcontracts, create purchase orders, etc. The bulk of the time is an external vendor working to deliver the item.
    – Adam Wuerl
    Commented Jun 15, 2015 at 5:04

2 Answers 2


If I understood your problem correctly, this is what I'd do: I'd split Task A into A1 and A2. A1 would have a planned duration value of x and A2 of y, where y represents the remaining duration that should finish within the five months of starting Task B. I would split task B into B1 and B2. When A1 finishes, both A2 and B1 starts. Both A2 and B1 will have a FS with B2. A2 and B1 should finish at the same time, i.e., they have the same planning duration, but if either slips then B2 start goes out.

If I completely misunderstood, clarify and then I'll try again.

  • 2
    Task A completes at the 5-month mark, so I don't need to break A into two tasks. I agree I can break B into two tasks: before A arrives and after A arrives. I was hoping to avoid this as I actually have a lot of B's being fed by the same A task and it's going to make various other things messy. Plus, I was hoping to learn more about how to use the lead/lag function. Thanks for providing a work-around though.
    – Adam Wuerl
    Commented Jun 14, 2015 at 0:43
  • 3
    Yeah, schedules get messy quickly. There are issues with MSProject using leads and lags. I am told it hoses up some of the calculations including critical path. One criterion of schedule health stipulates there are minimal leads and lags built in. I have that document somewhere and I will post when I find it. I still use but I try to create FS relationships without leads and lags as best I can. Good luck! Commented Jun 14, 2015 at 0:46
  • 1
    I found the document but not sure how to post it here. Nevertheless, you should be able to find it easily online. It's the GAO Schedule Assessment Guide, GAO-12-120G. Commented Jun 14, 2015 at 0:55

If I understand the problem correctly, my solution would be to split task A into 2 components: Procurement and Delivery. Procurement would have a short duration - in the illustration below I have given it 1 day - while delivery would be 2 months, representing the time taken for the supplier to deliver the component. By creating a Start - Start relationship between Task B and Task A Procurement, you show the start dates being aligned. By then creating a Finish - Finish relationship with 4 months gap, you can force Task A Delivery to finish 4 months before Task B finishes. You could also show it another way, using a Start - Finish relationship between Task B and Task A Delivery... I have shown this on the example below as Task C.

enter image description here

Does that address the problem?

  • I think the second method is closer to what I’m looking for because it directly encodes the 5-month span (rather than the 4-month duration from when A and B are completed. In this case 5 months is the actual constraint: some furnished piece of hardware is required 5-months after authority to proceed. This method seems to show the bars in the right place. I'd need to experiment and see if they move as expected if durations change.
    – Adam Wuerl
    Commented Jun 17, 2015 at 3:50

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