It's no different to any other job - you look at what your contract says and that's it. If you have no contract then look at what the default legal position is in your country / state.
In the UK I'd tend to consider 4 weeks "normal" both in terms of what a contract would say and what I'd expect but that may be very UK specific.
There are some situations where you might want to extend it a little if you think it's in your interest (normally that would be about not leaving on bad terms if there's a chance that it might damage your reputation to go earlier or not leaving other colleagues in the lurch) but that doesn't turn weeks into months.
As someone said, this isn't personal, this is business. Take a good honest look at how they've treated you - if you think they've gone above and beyond for you then you might reciprocate but the reality is that most businesses will act in their own interest and you should do likewise. If the owners / managers get offended by this then they're really not cut out for it.
In the UK I'd tend to consider 4 weeks "normal" both in terms of what a contract would say and what I'd expect but that may be very UK specific.
There are some situations where you might want to extend it a little if you think it's in your interest (normally that would be about not leaving on bad terms if there's a chance that it might damage your reputation to go earlier or not leaving other colleagues in the lurch) but that doesn't turn weeks into months.
As someone said, this isn't personal, this is business. Take a good honest look at how they've treated you - if you think they've gone above and beyond for you then you might reciprocate but the reality is that most businesses will act in their own interest and you should do likewise. If the owners / managers get offended by this then they're really not cut out for it.