Looking for your first CS job? Be sure to own your ideas (opens in new tab)

I think most employers will have a blanket "we own your IP" policy. But most of them will also make exceptions (and in writing) on a case-by-case basis once you prove you're a valuable employee. Because obviously you're not going to actually do anything on your own time if it's going to be your employer's property, whereas if you convince them that there's a potential for good PR with no real cost, they'll go for it. Once you've demonstrated that you're good at your job, and your side activities won't conflict with that.

Everything's negotiable, and IP is definitely something you should negotiate, but often there's a process for this that legal has approved and changing it is a dealbreaker.

A typical process is that you "disclaim" up front all the IP you take into the company, and they own everything after that.

A typical exception to that process that might be accepted is that they own everything related to their business that you come up with after you join the company.

An exception that can be pretty hard to get is that you own everything you come up with off-hours. This is reasonable, (though obviously you can disagree and turn the job down): if the company is providing you access to knowledge and domain exposure, you shouldn't be exploiting it to start your own business on the side. Also, it can be hard for them to pinpoint exactly when you came up with something, which creates legal headaches down the road.

The flipside is that if you're a founder, you'll have to deal with investors wanting the startup to own its IP.

I once signed on as a contract engineer (mechanical, not software) for a Fortune 100 company. My contract was actually with a contract agency that this company normally uses. I had negotiated the details of the job with my manager and then met with the onsite manager of the contract agency to deal with the paperwork. The lady got bent when I actually took about 45min to read every single line of the contract. She got even more huffy when I signed it but crossed out and initialed about 3 lines of the contract and handed it back. She claimed that I could not do that. I told her to talk to my manager and run it by legal (I knew they really needed my skill set) and get them to initial the crossouts and mail me a copy. The lines that I crossed out legally claimed anything I might invent, create or produce at work or off-hours for the terms of my employment. So if I invented the proverbial better mouse trap on my own time this Fortune 100 company would have moved up a few notches and I would get my salary. Legal signed off on my edits and I went to work. So the moral of the story is don't be intimidated into signing something you don't understand and don't be afraid to seek changes to the contract if it is not acceptible.

Many states have limits on what bits of IP agreements can be enforced.

Regardless of the IP agreement, the important thing is to be at least a little careful. If you have a new, world changing piece of software you're writing, do it on your own time with your own resources. Avoid doing anything at all with it on company time, and don't use your company owned laptop to do development.