Roth Conversion Calculators

[Guest breezer]

The majority of the roth conversion calculators request that you input marginal tax rate for conversion years and distribution years. The marginal rate is accurate for conversion years since conversion amount will be in addition to AGI. My problem is that in distrbution years the marginal tax rate will overstate total taxes since there will be no additional earned income. Wouldn't it be more accurate to use effective tax rate at distribution?

For example a $75,000 annual distribution would have a marginal rate of 28% but an effective rate of 21% for an individual filling married/jointly. Utilizing the effective tax rate on the distribution yeilds a much different answer in the conversion calculations.

In a general analysis why would it be advantageous to pay 28% taxes now rather than 21% later?