Stop right there.
Using another job offer as a bargaining chip may be tempting, but too often, it ends badly. If you want a raise, then negotiate it on your own merits—or prepare to move on.
1. Employers often make counteroffers in a moment of panic. ("We can't have Joe leave right now! We have that big conference next month.") But after the initial relief passes, you may find your relationship with your employer—and your standing with the company—has fundamentally changed. You're now the one who was looking to leave. You're no longer part of the inner circle, and you might be at the top of the list if your company needs to make cutbacks in the future.
2. Even worse, your company might just want time to search for a replacement, figuring that it's only a matter of time until you start looking around again. You might turn down your other offer and accept your employer's counteroffer only to find yourself pushed out soon afterward. In fact, the rule of thumb among recruiters is that 70 to 80 percent of people who accept counteroffers either leave or are let go within a year.
3. There's a reason you started job-searching in the first place. While more money is always a motivator, more often, there are also other factors that drove you to look: personality fit, dislike of your boss, boredom with the work, lack of recognition, insane deadlines—whatever it might have been. Those factors aren't going change, and will likely start bothering you again as soon as the glow from your raise wears off.
4. Even if you get more money out of your company now, think about what it took to get it. You needed to have one foot out the door to get paid the wage you wanted, and there's no reason to think that future salary increases will be any easier. The next time you want a raise, you might even be refused altogether on the grounds that "we just gave you that big increase when you were thinking about leaving."
5. You may be told to take the other offer, even if you don't really want it—and then you'll have to follow through. Using another offer as a bluff is a really dangerous game.
6. Good luck getting that new employer to ever consider you again. If you go all the way through their hiring process only to accept a counteroffer from your current employer, then the former is going to be wary of considering you in the future. If it's a company you'd like to work with, you might be shutting a door you'd rather keep open.
Now, are there times where accepting a counteroffer makes sense and works out? Sure, there are always exceptions. But it's a bad idea frequently enough that you should be very, very cautious before doing so.
Alison Green writes the popular Ask a Manager blog, where she dispenses advice on career, job search, and management issues. She's also the author of Managing to Change the World: The Nonprofit Leader's Guide to Getting Results and former chief of staff of a successful nonprofit organization, where she oversaw day-to-day staff management, hiring, firing, and employee development.