If your client or company is in the process of preparing a District of Columbia (DC) combined return due October 15, 2012, then you probably are experiencing the pain of working through the regulations and calculations.  Especially since the regulations just became final and there are conflicts between the regulations and the statute. 

Hence, to provide a little guidance and assistance, I thought I would provide a "cliff notes" version of some of the main points (at a high-level) from the regulations.  If the following affect your client or your company, please review the regulations for more details:

1.  Not a nexus combination (includes all entities that meet the requirements for inclusion regardless of nexus)
2.  Combined return includes unincorporated businesses, transportation and financial companies
3.  Excludes:  insurance companies, exempt entities, qualified high tech companies, and 80/20 companies
4.  Companies must be commonly controlled ( > 50%)
5.  May have one or more unitary businesses or combined groups
6.  Commmon owner need NOT be included in the combined group
7.  Passive holding companies MAY be included
8.  Instant unity NOT presumed, but may be proven
9.  Waters-edge method is the STANDARD filing method
10.  Worldwide method is an election (binding for current year and next 9 years)
11.  Prior net operating losses may NOT be shared among members of group
12.  Tax credits may NOT be shared
13.  Single member LLCs are disregarded
14.  Minimum tax applies to each taxpayer member
15.  REITs and RICs allowed dividends paid deduction
16.  FAS 109 deduction is claimed over 7 year period beginning in 2015 (file form with 2012 return claiming amount)
17.  Adopts the Joyce rule for apportionment purposes

There are many issues surrounding the combined return regulations that are causing confusion and a lack of clarity.  One of the main problem areas is understanding how an unincorporated business and its owners are included in a combined return.  If your client or company has this issue, please consult the regulations and a state and local tax advisor for assistance.