so, how does one figure what percent they should claim
one way would be based on the time used for your SE work divided by the total time used.
or hours used for SE work divided by total hours in the year (being conservative)
now you probably haven't kept any such records, so it's either forgo the deduction or guess.
the IRS doesn't like guesses so if they ask for documentation that you can't provide they can disallow up to the full amount you deduct. it's really at the auditor's discretion.
