It wouldn't hurt to include with a mailed tax return either a manually prepared Form 8606, clearly marking the form as being for calculating the taxable amount of a distribution from an inherited traditional IRA, or provide the same calculation on a separate explanation statement. Without some sort of supporting calculation, the IRS is likely to question why the distribution was not fully taxable. Providing that information may head off an IRS query when an IRS examiner looks at your tax return after having been kicked out by the IRS Automated Underreporter Program, which seems likely to happen.
