this is a myth I am always questioning.

The double tax on borrowing 401k interest is a reason for many people to against borrowing 401k.

On the other hand, people has to know that the interest goes to 401k account. Yes, it will be taxed again when you take it out. But if the borrower gets the loan from bank, the interest paid on the loan will goes to the bank. It is 100% gone, which is wrose than double tax.

Therefore, I would not worry about double tax issue with 401k loan.