There's a separate five-year rule that applies only to those who convert other types of retirement accounts into Roth IRAs. Here, the idea of the rule is to prevent people from using Roth conversions to get penalty-free access to their traditional retirement accounts.
This five-year rule also starts the clock on Jan. 1 of the year in which you do the conversion. As a result, those who convert late in the year only have to wait a bit longer than four years before taking withdrawals.
However, this five-year rule is different in that it applies separately to each Roth conversion you do. Each new conversion starts its own five-year clock, and you'll need to account for multiple conversions to make sure you don't take out too much money too soon.
Note that the five-year rule applies equally to Roth conversions for both pre-tax and after-tax funds in a traditional IRA. That means, if you're using the backdoor Roth IRA strategy every year, your "Roth contributions" are really conversions, and you can't withdraw them for five years without penalty.
