What the title says. How much extra income would you have to have on a monthly basis to make working worth it?

I'm working part time and it pays for the nanny and preschool (which we were paying for regardless of whether I worked)...and a few other things. But since I'm only part time, it's certainly not a windfall. But I'm doing it to stay relevant in my field, to have something outside of the home, and because I think I'm a better mom when not with my kids 24/7.

I'm curious what you'd have to earn to make working feel worth it to you.