This is a different conversation than negotiating a new offer
Negotiating pay for a new role happens against competing offers and external market comparisons. Asking for a raise in your current job is closer to making a persuasive case for what you've contributed and the role you want next -- concrete evidence beats an emotional appeal every time.
A running list of accomplishments makes this easier
Keeping an updated, reverse-chronological list of project outcomes -- the same habit that helps when writing a resume summary -- gives you ready-made evidence for a raise conversation, and doubles as a head start if you ever start job hunting.
Frequently Asked Questions
I've only been here a few months -- is it too early to ask?
Generally it's easier to make a persuasive case after roughly six months to a year of visible results. That said, if your actual role has grown well beyond what was agreed at hiring, it's reasonable to start the conversation earlier.
If I get turned down, should I start job hunting right away?
One "no" isn't automatically a signal to leave. Find out the reason and when it will be revisited, give it fair time, and only weigh other options if nothing changes after that.