The calculation is the easy part
The series generally must continue until the later of five years from the first payment or age 59½. An impermissible modification before that date can cause the additional tax that was avoided in prior years to be recaptured, with interest. Death and disability have separate statutory treatment; do not treat those exceptions as planning defaults.
The RMD method is recalculated annually. Notice 2022-6 also preserves a one-time switch from the fixed amortization or fixed annuitization method to the RMD method. Other changes to the payment stream can be a modification. Taxable distributions are generally included in ordinary income; the SEPP exception addresses the additional 10% tax, not ordinary income tax.
Why this calculator caps the rate at 5%
Under Notice 2022-6, a reasonable rate is not more than the greater of 5% or 120% of the federal mid-term rate for either of the two preceding months before the first distribution. A live 120% federal mid-term rate depends on the actual start month. Rather than guess that moving value, this calculator supports the always-available 0%–5% comparison range and stops above it. If a higher rate may apply, bring the date-specific IRS revenue ruling to a tax professional.
This calculator does not provide tax advice and does not constitute a personalized recommendation. Verify the full series with a qualified CPA, enrolled agent, or tax attorney before instructing a custodian.