Cecil Cammack's Inter-Est estate tax computation program was the most comprehensive solution to this problem. However, because of the variables inherent in these computations, the user had a tremendous choice of data input options. Inter-Est therefore did not indicate whether a particular input item or flag setting might be improper - it simply ran the computation in whatever manner the user might have designated. An user would therefore not know if the answers generated by a computation were correct for his or her purposes unless they also had sufficient knowledge to understand how section 6166 computations should function.
The Inter-Est program and Cecil Cammack's website are no longer available on the Internet. The last Inter-Est Release version was 127f, which incorporated tax law changes effective for 2013 and 2014 dates of death. Existing copies of Release 127f can be manually updated with changes to the annual inflation factors and exemption equivalents so that the program can continue to be used for dates of death after 2014 for as long as there is no change in either the tax rate schedule or the substantive estate tax law.
We used parallel Inter-Est and Excel spreadsheet computations for many of the older examples. Our basic interrelated computations in 2010 were run with the Inter-Est program, which was then officially used by field IRS Estate Tax Attorneys. However, in 2010 they began using the Notebook application for field examination interrelated computations instead of Inter-Est. Today, IRS Estate Tax Attorneys are not authorized to use Inter-Est for their field examination computations. The Notebook computation application is used by Estate Tax Attorneys nationwide. Although this is also true for Cincinnati Campus, Inter-Est can still be used by IRS personnel at Cincinnati Campus under some circumstances.
Parts of the more recent computation examples on this site replicate the IRS Notebook examination report format.
As an historical note, until 2010 IRS Estate Tax Attorneys in the central part of the United States generally used an internally developed Excel spreadsheet application for field examination tax computations rather than the Inter-Est program. Many features of that Excel program were carried over into the Notebook application.