Can a taxpayer convert only nondeductible IRA basis tax-free?

Not automatically. If the taxpayer has other traditional, SEP, or SIMPLE IRA balances, the conversion is generally computed using pro-rata logic. The nontaxable portion is based on the taxpayer's after-tax IRA basis compared with the total IRA pool used in the Form 8606 calculation.

For example, if a taxpayer has USD 6,000 of basis and USD 54,000 of total relevant IRA value, basis is only 10 percent of the pool. A USD 12,000 conversion would be only about USD 1,200 nontaxable under that simplified ratio, not USD 6,000 tax-free by choice.