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# Problems with how Project calculates Duration

## Problems with how Project calculates Duration

(OP)
I would like Duration to automatically calculate based on Work and Resources.  Project seems to work fine, when using one resource, but using multiple resources, the Duration calculation appears to be off.  As an example, I will create a task for 10d (80hrs), and add two resources (one full-time and one part-time), at 75% each (9hrs/day combined).  I would assume the Duration would calculate to 8.88d(80hrs/9hrs) and an End Date of 4/20/06 (if started on 4/10/06), but it instead calculates to 9.92d.  Not only that, but the End Date is calculated to 4/28/06 (which is 15 business days long).  What am I missing?

### RE: Problems with how Project calculates Duration

how are you entering the data and in what order?

your statement about "9hrs/day combined" does not jibe with "75% each," which should be more like 12hrs/day combined

In any case with a[1],b[0.125], I get 8.85 days for 80 hrs of work.

TTFN

### RE: Problems with how Project calculates Duration

(OP)
I'll try to reword.  I have one full-time resource (8hrs/day).  That resource can only spend 75% of their time on the task (6hrs/day).  I have another resource, which is a part-time resource (4hrs/day).  That resource also can only spend 75% of their time on the task (3hrs/day).  The 6hrs + 3hrs is where I was getting the 9hrs (or (8+4)*.75%).  Hope that makes more sense.

As for the entering of data, I have tried multiple different orders.  I've tried work, resource 1, and then resource 2, and duration still does not calculate based on how I think it should.

Thanks

### RE: Problems with how Project calculates Duration

You must enter both resources AT THE SAME TIME

TTFN

### RE: Problems with how Project calculates Duration

(OP)
I tried it multiple different ways, and here are the results:
1) Add Resource 1 @ 75%, and then add Resource 2 @ 75%.  Duration calculates at 9.83d.  The difference between the Start and End Dates is 13d.
2) Add Resource 1 and Resource 2 @ 100%, then change Resource 1 % to 75%, and then change Resource 2 % to 75%.  Duration calculates at 10d.  The difference between the Start and End Dates is 14d.
3) Add Resoucre 1, then add Resource 2, then change Resource 1 % to 75%, and then change Resource 2 % to 75%.  Duration calculates at 1017d.  The difference between the Start and End Dates is 14d.
4) Add Resource 1 @ 113% (which is really what Resource 1 and Resource 2 are at 75%).  Duration calculates at 8.85d.  The difference between the Start and End Dates is 9d.  This is the one that calculates correctly.  I would think the first three would calculate the same way.

To setup a part-time resource, I'm using the calendar, setting them to work 4hrs/day (8am - 12pm).  Based on this, I'm assuming I can work this resource at 75%, which would be a total of 3hrs.

Thanks

### RE: Problems with how Project calculates Duration

No, you need to enter all the correct values at the same time!

you type r1[0.75],r2[0.75] in ONE OPERATION.  DO NOT EDIT, DO NOT CHANGE.

TTFN

### RE: Problems with how Project calculates Duration

(OP)
It calculates the same as option 3 above.  No difference.

### RE: Problems with how Project calculates Duration

then you need to split the task

TTFN

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