I'm in the biopharma industry and have been offered a position in a startup biotech company offering 21% more than I make now. Of course, I accepted that offer as I currently dislike my role, but tomorrow I have an interview for an internal promotional opportunity. I told the other company I won't be able to start until mid-October, so that gives me some time left at my current company, where I have yet to put in notice (and don't plan on it).
Should I be offered a promotional opportunity at my current company, I do believe the wage they'd probably offer me is on par with, if not less than, the wage the other company is offering. I was wondering what is the best way out there to leverage my offer that I accepted at my other company to gain an upper hand in negotiating a better pay that might otherwise convince me to stay.