Complexity is simply the factor by which the historical or reference effort is multiplied to derive the new effort. It is set based on a subjective assessment of the "relative complexity" of the new vs. old deliverable. For example if the old deliverable was a login screen with single factor authentication and the new deliverable is the same login screen but with two factor authentication then the complexity factor might be 25% or 1.25.

Complexity factor is entered as the ratio of old vs. new e.g. 1.25 means "old effort plus 25%" or "old effort times 1.25". Complexity factors can be less than 1 but cannot be 0. If not input or set as 0 then the complexity factor is taken as 1

There are essentially three use-cases for complexity factor in this application:

1. When copying an estimate from a previous estimate (copy plan) then the complexity is the factor applied to the historical estimate to derive the new effort. It is also called a "similar-to" factor
2. When copying an estimate from performance history (copy actuals) then the complexity is the factor applied to the actual labor hours recorded to derive the new effort. It is again called a"similar-to" factor
3. When estimating the cost of a make part the complexity factor is the factor applied to the routing standards for one unit to derive the unit time, by resource, for the new part. It is again called a "similar-to" factor and represents the extra effort or complexity to build the new part vs the old one.