I don't mind this question, but already predicting a 10 pager of Smashsuperman or whatever his name is talking about Hulk having no limit because he lifted a rock 3x the size of earth in one of his own drawings.
That aside it's said he has no limit, but I do feel there is some limit, but it's probably more than he'll ever need. Reason I say this is because characters have had no limits in areas before and met them, take Juggernaut, not kinda unstoppable, but totally unable to be stopped once started, then he was stopped. It took a lot to stop Juggernaut, and many many years for it to happen, but it did. It may not be in our life times (if comics last that long lol, or if Hulk comics still exist), but I have a feeling there will eventually be a story of Hulk lifting or holding something back, getting ticked and stronger, then captions saying "After hours of struggling Hulk had no more strength left in his body, his limit was reached" or something. Outside of my guess tho, no acutal limit has yet to been shown, though he hasn't been put in situations to really really test it like having to keep two planets from colliding or something.