The existence of a thousand white swans does not prove there are no black swans. But the existence of one black swan (many are found in Australia) proves that not all swans are white. I am not looking for a black swan, I’m looking for an example, preferably not hypothetical, of when a Roth conversion is a good idea.

I asked this in another thread, to which someone replied astutely, “To do this, wouldn't you need to calculate tax savings and tax costs and indirect financial costs (from the Roth conversion tax) and savings related to differing uses of tax savings over a very long period of time? I'm not being sarcastic or facetious.”

Exactly. And that suggests one example. Say a resident of Florida plans to retire to New York, because they miss snowy winters and flooded subway trains in summer. They know that their state tax rate will be higher, so they act now to avoid it. But how often does that happen? Likewise, someone expecting a higher federal tax bracket next year – perhaps a lottery winner, or a lucky heiress – might use up some of the lower bracket this year.

But as I recently wrote a client, “Let's say you are in a 20% tax bracket, now and in six years. You have $100K you can convert to a Roth. Do it and you're left with $80K. If that grows at 8% for 10 years, it becomes $172,720 that you can withdraw tax-free. If you keep the whole $100K it becomes $215,900. Withdraw it, and pay 20% tax on that, you still have $172,720. Notice how it comes out to the same number.”

And I added that I have seen clients “need assisted-living that qualifies as a medical expense (so IRA distributions to pay for it are not taxable). Hope for the best but plan for the worst.”

But most of the time, I wonder if brokers get credit for every new account they open, even if they involve depleting the client’s net worth through a Roth conversion.