While Roth IRAs are very popular as a retirement savings vehicle due to their tax-free growth treatment, they also have several unique rules associated with them to ensure that their favorable tax status is not abused. In particular, there are two different 5-year rules associated with Roth accounts to prevent them from being taken advantage of; the first 5-year rule applies to Roth contributions and determines whether earnings will be tax-free, while the second 5-year rule applies to Roth conversions and determines whether conversion principal will be penalty-free.
Each of the 5-year rules are measured from the beginning of the tax year for which they apply, which means in reality tax-free earnings or penalty-free conversion principal may be accessible in less than 5 years in certain circumstances. And because the Roth rules aggregate all accounts together for the purposes of determining the tax treatment of various distributions, it's necessary to track the various 5-year rules and the amounts they're associated with, regardless of whether they are held separately or mingled together into a single account.
Ultimately, being able to effectively navigate the various Roth 5-year rules creates several planning opportunities as well. For some, taking advantage of the Roth conversion 5-year rule is a way for those well under age 59 1/2 to tap their IRA funds "early" without an early withdrawal penalty. For others, the reality is that the Roth conversion 5-year rule is a moot point anyway, because they already meet another exception to the early withdrawal penalty (e.g., already being over age 59 1/2). However, in all cases, the 5-year rule for contributions must be met before any Roth earnings can actually be tapped tax-free; fortunately, though, because any first-time contribution or conversion can start the clock, clients who are concerned about the 5-year rule can make a contribution to a Roth (or to a traditional IRA and then convert it) to start the time window now, and ensure they'll never need to worry about it in the future!