There is no firm rule. But there is this statement from the IRS: "The IRS presumes that an activity is carried on for profit if it makes a profit during at least three of the last five tax years, including the current year — at least two of the last seven years for activities that consist primarily of breeding, showing, training or racing horses." Note that the 3 out of 5 statement is a guideline, not a rule and that all other factors must be taken into consideration.
Reference: https://www.thebalancesmb.com/is-this-business-for-real-or-is-it-a-hobby-397675
Additional Reference:
https://turbotax.intuit.com/tax-tips/small-business-taxes/when-the-irs-classifies-your-business-as-...
