Cobra Help

Calculate Forecast Spread by Budget

A set of examples may help demonstrate how Cobra calculates forecast spread according to the current spread.

Assume that you have the following budgeted and forecast costs before statusing:

Periods 1 2 3 4 5 Total
Budget 100 200 300 200 200 1000
ETC 100 200 300 200 200 1000

After one period, assume that ETC has been calculated as follows:

ETC = BAC Earned Value = 1000 - 50 = 950

This results in the following cost data:

Periods 1 2 3 4 5 Total
Budget 100 200 300 200 200 1000
Earned Value 50 50
Actual Costs 100 100
ETC 211 317 211 211 950

Now, if the estimated finish date for the work package had been pushed back one period (to take the poor performance into account), the spread would be:

Periods 1 2 3 4 5 6 Total
Budget 100 200 300 200 200 1000
ETC 95 190 285 190 190 950

Note, however, that the profile used depends on how much has been earned. Because the earned value was less than the amount of the first period budget, the entire budget profile was used. If, however, the full amount had been earned, the profile used would have been generated from the last four periods of budget. For example, assume a performance factor of 1 and the following cost data:

Periods 1 2 3 4 5 6 Total
Budget 100 200 300 200 200 1000
Earned Value 100 100
Actual Costs 120 120

First, the spread profile curve is created. It is a four-point curve made up of the values of the last four budget amounts: 200, 300, 200, and 200, which total 900. The profile therefore is:

  • Period 2 .222
  • Period 3 .333
  • Period 4 .222
  • Period 5 .222

If expressed as a cumulative curve:

  • Period 2 .222
  • Period 3 .555
  • Period 4 .777
  • Period 5 1.0

The ETC profile is then calculated by determining each spread point:

FieldDescription
First spread point
  • Factor= 4 \* (1/5) =.8
  • Integer= 0
  • Modulus =.8
  • Percent= 0 + (.8 \* (.222 - 0)) =.178
Second spread point
  • Factor= 4 \* (2/5) = 1.6
  • Integer= 1
  • Modulus =.6
  • Percent =.222 + (.6 \* (.555 -.222)) =.422
Third spread point
  • Factor= 4 \* (3/5) = 2.4
  • Integer = 2
  • Modulus=.4
  • Percent=.555 + (.4 \* (.777 -.555)) =.644
Fourth spread point
  • Factor = 4 \* 4/5 = 3.2
  • Integer = 3
  • Modulus=.2
  • Percent =.777 + (.2 \* (1 -.777)) =.821
Fifth spread point
  • Factor= 4 \* (5/5) = 4
  • Integer= 4
  • Modulus= 0
  • Percent= 1

These spread points are then multiplied by the ETC amount to get cumulative spread values for the ETC, and the interval values are then obtained by subtraction of the previous value:

Periods 1 2 3 4 5 6 Total
Budget 100 200 300 200 200 1000
ETC 160 220 200 160 160 900

How to...

Create a Forecast

Set Up a Retain EAC Forecast with the Scale EAC Option

Copy Budget to a Manual Forecast Using the Reclass Wizard

Learn more about...

Forecast Preferences

Calculate Forecast Process

Parent Topic:

How Cobra Spreads ETC