@UncaNed It was in response to a scenario I proposed of converting exactly $6k of a traditional IRA to Roth IRA. Such as one would do with a maximum ‘backdoor’ roth contribution but
@MP3Mike was pointing out the pro-rata rule on conversions doesn’t allow ‘backdoor’ technique for all situations. Specifically the illustration is if you have $6k of post tax contributions and $54k of gains in traditional IRAs converting only $6k (not converting the full $60k) the tax treatment is pro-rata so of the $6k conversion $5400 is taxable.