Trying to choose Pretax vs. Roth 401(k)? Why it's trickier than you think, experts say

The easy answer is always to look into your crystal ball and see what your financial situation will be in retirement. If the RMDs from your retirement funds, social security, military retirement and other taxable income will have you in a high tax bracket, go with a Roth otherwise, go with a traditional.

However that answer always relies on that magic crystal ball which is nothing more than a pseudo-scientific guess at what the future holds based on a gut feeling of what the future will hold or a holistic look at your financial situation with many assumptions for the future thrown in.

In either case, it's a guess about the future which is why advice is subjective - you will be relying on someone else's gut or assumptions about your future.

I will say that for most systematic savers that have an almost pathological revulsion to carrying 'unnecessary debt' - those type of individuals will be well suited to having a Roth 401k/IRA.

If you are the type that lives for today and looks to have 'just enough' to keep yourself comfortable in retirement - those should almost always opt for the traditional 401k/IRA.

If you're in-between - roll the dice and chose your path. Regardless of which way you chose though, either is MUCH better than doing neither. The discussion between a traditional vs Roth fund is a discussion about "which of my two good options will be the best for me?", not "which is the good choice and which will be bad?".

If your crystal ball is broke your future self and you don't accurately project your future-self situation, you might not keep as much money as you would if you had prognosticated correctly, but you'll still have a lot more than if you didn't do either.