(10000 * (1.05^10) - 10000) * .67 = 4213. 14213/(1.032^10) = 10372; or about a .36% return. Not surprising that a lower tax rate gets to the same number soone

(10000 * (1.05^10) - 10000) * .67 = 4213. 14213/(1.032^10) = 10372; or about a .36% return. Not surprising that a lower tax rate gets to the same number sooner through compounding. BUt the bigger issue is that you have to pay tax on interest as it is accrued, not all at the end. So in your case there's a 3.35% return vs. 3.2% inflation or a .15% net return.