It's really tempting to slack off on the PhD when you get a big contract, but if you're serious about the PhD do not put it second. If you're in classes still,

It's really tempting to slack off on the PhD when you get a big contract, but if you're serious about the PhD do not put it second. If you're in classes still, you should be good for a while, but once you get into research it will really depend on your advisor. e.g. I worked on research all-out 3 days a week and then had 2-3 full days each week to freelance while still maintaining a social life. Also, depending on your stipend, be selective with clients. If they seem like jerks don't take on the added stress. It's one benefit of moonlighting when you don't NEED the money to pay the bills.