Totally dumb advice. I've tried to be the good guy several times and give my current employer a month of my time to crunch and write docs or whatever. It's usually stressful and doesn't make a huge impact in the end. Better to just offer 2 weeks and move to new role as fast as you can. Your new employer usually wants you to start ASAP, and they are what matters now that you already made the choice to move on.