I keep statistics on my success rate in the United States Tax Court, since the information is easy to keep track ofonline. The numbers are laid out in the table below.
Cases where I was able to reduce the tax bill: 93%
Average reduction (dollar amount): $23,871
Average reduction (percentage): 60%
Of course, this is just for IRS matters which were petitioned to the United States Tax Court. (most are not - tax disputes are usually resolved within the Internal Revenue Service without needing to take legal action) Nonetheless, this data can give you an idea of what to expect. As you can see, tax disputes often result in a compromise.