Ask HN: Yrs exp SDE, how much should I charge?

Hello HN! For the past 15 years, I've been working as a Software Developer Engineer. I've focused mostly in back-end languages, and also a bit of front-end (though I'm not up-to-date with the latest Front-End trends). I have added a lot of value to the companies I've worked for, but I have the feeling I've never been compensated fairly. 1) My question for you guys is: how much should I charge per hour? 2) Is there a way to finding clients or companies that pay better wages? Thanks!