I thought SS allowed even 5% amounts for withholding, but Double-checking what SS allows now...they will only accept 7, 10, 12 or 22% (or none) ...so you'd have to choose from those.
https://www.ssa.gov/benefits/retirement/planner/taxwithold.html
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
