if you wish to convert tax free to Roth, your entire value of all your IRAs must be no more than your basis which is the non-deductible part,
Otherwise, it cannot be 100% tax free nor 100% taxable because a Traditional IRA distribution or conversion always has a basis fractional part and a taxable fractional part as calculated on Form 8606.
You must use Form 8606 to arrive at your new prior years basis.
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