Upvote:2
There is none. However, the more recent time in the US you have, the more likely you are to receive additional scrutiny and possibly be denied entry. The likelihood also depends on the purpose and planned duration of your second visit.
I'm looking for an official source and will add it when I find it.
Upvote:9
Contrary to the Schengen 90/180 rule, there is no hard rule for this, but:
Of course, it all depends on how long you are planning to stay, what you say you are going to do in the US, your ties to your home country, etc. The CBP officer will decide when you arrive.