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Why invest in IRA while a low-cost index fund is much simpler?
The advantage of an IRA (or 401k) is you get taxed effectively one time on your income, whereas you get taxed effectively multiple times on some of the money in a taxable account. You have to consider it from the perspective of time value of money -- the concept that an amount of money now is the same value as a greater amount of money in the future. And in fact, if you put your money in an investment, the principal at the start can be considered the same value as the principal + earnings at the end. In both Traditional and Roth IRA, you pay taxes on the entire value of money once (remember that the principal when depositing is the same value as the principal + earnings when withdrawing). The only difference is when (year deposited or year withdrawn), so the main difference between the two is the tax rate when depositing vs. tax rate when withdrawing. I'll give you an example to demonstrate. We will assume you invest $1000 of pre-tax wages, it grows at 5% per year, there's a 25% flat tax now and in the future, you withdraw it after 20 years, and withdrawals are not subject to any penalty.