How Traditional IRA's tax deferral works
Traditional IRA is a tax timing strategy: you get a deduction when you contribute (based on your current marginal rate) and pay tax when you withdraw (based on your retirement marginal rate).
The account grows tax-deferred in between — no taxes on dividends, interest, or capital gains as long as the money stays in the IRA.
This is valuable because it lets more of your gross return compound, and because you control the timing of when the tax bill comes due.
If you expect a lower tax rate in retirement, Traditional is mathematically better; if you expect a higher rate, Roth wins.