Just one example of algebra at work.That's an interesting result that I hadn't really realized.
Few people have the faintest idea what their effective tax rate it and even less of an idea how to figure it out.
In round numbers the median income in the U.S. is about $50,000. Someone single making that amount and not claiming anything other than the standard deduction and exemption will have a taxable income of $39,600, which places them in the 25% marginal tax bracket. However, their federal income tax is $5,639, for an effective tax rate of just 11.3%. The ubiquitous family of four is in the 15% bracket but their tax liability is $2,233 for an effective tax rate of just 4.5%.
This is leveraged even further in retirement. If your income is purely from retirement savings and Social Security, then you will no longer be paying the FICA tax, so now your gross income only needs to be $46,175 to be comparable. A person that makes this level of income (i.e., about median) their entire working life will have a SS income of about $20,000/yr, so they need to draw the remaining $26,175 from their IRA to cover this. The single person is in the 15% bracket but will only pay $1,900 in taxes, or 7.3% of their distribution. But arguable a more apples to apples way of viewing it is that they are paying that $1900 to keep a $50,000 lifestyle, or 3.8%. Which way makes more sense depends on exactly what you are looking at.
But the family has an even better situation. Assuming they are now a family of two (the kids aren't living in the basement) and one spouse claims half the other spouse's benefit, then they only need to withdraw $16,175 and that isn't even close to their combined deduction/exemption of $20,850. So they don't owe ANY taxes on their traditional IRA savings, at EITHER end. But they would have paid 15% up front on a Roth.
That's not to say that a Traditional always beats a Roth -- it doesn't, but it does most of the time for most people. Drawing too much from a Traditional can make some of your Social Security benefits taxable, for instance. Also, in early years when you aren't making much, a Roth can make a lot of sense. My daughter is working for me and 90% of her wages are going into a Roth. Since she has NO payroll tax or income tax at her earnings level, all of those funds will never be taxed (assuming they don't change the law, which I fully expect they will at some point).
The best strategy is to have a well-crafted blend that reflects all of your income sources in retirement and how they interact from a tax standpoint so that you can withdraw from Traditional accounts up to the point of being taxed (including SS benefits) and then draw from Roth above that. Even that isn't the truly optimal line, but it is in the ballpark.