[itamarst]

Definitely want to do some research up front to rule out places where it will never fly. But- negotiating shorter workweek is different than negotiating salary (in most countries, anyway).

My experience, as well as others I've heard from, is that if you say upfront "I want fewer hours" companies will just say "no". This is not as much an issue with salary, because there's diversity of salaries, but pretty much no companies will hire you for 4 days without extra negotiation. So: if you ask for 4 day workweek upfront the vast majority of companies will just walk away.

On the other hand, if you keep your mouth shut, once you have an offer already you're in a different situation. Worked for me, as well as person I interviewed who has done this way more than I have. The company has decided they like you, you've impressed them, now they're in "what do we do to hire this person" mode. So if you ask at that point they're much more likely to say "yes".