Let’s say the Joneses defer $500,000 in a 401(k) earning 7.2%. Great—it doubles to $1 million in 10 years. At retirement, they want to live off the interest: $72,000 a year. But here’s the catch: it’s all taxable. In a 33% combined tax bracket, they lose $24,000 to Uncle Sam—netting just $48,000. That’s only $4,000…