In the event that I get a job offer while employed and my current employer offers me a raise to stay instead of moving to the new job, should I request that the raise be in writing? Some advice on The Workplace says to never accept the counter offer, but in the event that I want to, or at least to be able to present it as proof that my current employer will pay a certain amount for me, it seems as though written proof would be a good idea. In the past when I received a raise all I got was a small slip of paper after the fact.
Firstly, unless you want to stay with your current employer, I recommend that you simply accept the offer from the new company. By presenting a counter offer from your existing company you run the risk of having the new company either refuse to match it, or even revoke their offer.
While it does risk creating a sense of mistrust, I recommend getting the counter offer in writing. If they won't provide that, tell them you won't stay and take the other offer.
My reasoning is based on personal experience from many years ago: I had been in a job about 11 months. The employer I had left made me an offer to return that would have been a huge (25%) raise. I preferred the newer job, but the size of the offer from my former employer made it difficult to turn down. Thus, I talked to my boss, telling her I wanted to stay, but felt the other offer was too good to turn down. She said she couldn't match the offer, but could come close. The counter offer was enough that the difference (along with better benefits and the more satisfying job) was not enough to make me take the offer to return to the old company. However, my boss also said I would have to wait until my annual review to get the raise; since that was only 1 month away, I accepted the situation and told my old employer that I was staying where I was. The review itself went well; however, when my paycheck was supposed to arrive with the new raise, the boss called me into her office. Her boss had refused to approve the raise she and I had agreed to; I was still getting a raise, but it was only about 1/3 of the raise I expected.
Executive Summary: If I were you, I'd have the signed revised contract in front of me (effective the date of signing), and would expect them to exceed the offer from the other company rather than just match it. So yes, I would get it in writing.
This being said, I've worked without contracts for months because I've trusted my employer will do the right thing, and have never been burned. Regardless of what you decide, you should think about the following:
Caveat #1: Your Leverage
In your current situation you have leverage only from the fact that you have a concrete (time-limited) offer from another company. The second that you turn down the other company you are at the mercy of your current employer. After you turn down the other job, your last resort option goes from having a job waiting with a better salary, to being unemployed until you can find another job.
Caveat #2: Can Your Manager Make that Decision?
Many companies do not empower managers below a certain level to agree to raises without review. And many companies will only provide raises at certain times of year (during reviews) when they can evaluate the cash flow of the business as a whole and make an educated decision about how well the business is doing, and how much should be translated to wage increases for the workers.
What this means is that your manager may be well-meaning when they offer you the raise, but if they don't have the authority within the organization to actually provide that raise, you may end up like @GreenMatt suggested and be stuck with empty promises that don't come to fruition (and have blown some goodwill with the other company that offered you a job).
Caveat #3: Will They Really Offer the Same Salary?
Presumably if you take this other job, you will immediately start receiving the new salary, and then will be given a regular raise during the review period. Your current employer may very well say, "This year we've already given you a raise, so we won't be giving you the regular raise during the review period" when it comes around to it. And this makes sense to them -- they've gotten you to stick around, and it'll be tough saying, "Yeah, we need another 5% on the already 20% increased salary for employee X, because he did a good job this year."
If you don't have a signed contract and immediate raise, do you trust that the company will really give you that increase pro rata from the time of the agreement, or will they assume that since you've lost your leverage, losing 3 months of a raise is something that you can live with in the time being? In a year will you really be prepared to quit if they give you a lowball offer for regular salary increase?
Caveat #4: Why Give a Raise Now?
If your company thought you were that valuable, they could have already given you a raise. But they didn't. Why not? If it is just a lack of knowledge of your market value, then that could just be an honest mistake. If they are constantly hiring, however, they definitely knew your market value and just didn't want to pay it. Do you think that attitude will bode well for your future? Do you think you will constantly be able to leverage other job offers against your company, and they will keep paying out?
If a company can get away with lowballing employees on salary, they will not be happy with you pushing back (even if your performance is good). At some point, you will likely have to jump ship to get paid what you're worth. If you're okay with repeating this process down the line, no problem, but be sure you keep that in mind when you make this decision. You said you want to stay, and that's your choice, but just think about the bigger picture rather than your next paycheck.
If you want to accept the counter, then you presumably trust the individual making the offer. If that is the case, then you should not ask for the offer in writing because they will infer that you don't trust them (as they have previously had a less formal way of confirming your raises).
If you want to accept the counter but do not trust the individual making the offer, then you should ask for it in writing and accept that they will know that you don't trust them and/or the organization.
I would suggest that if you choose to ask for the offer in writing you will only amplify any misgivings about you as an employee caused by your stated intention to leave.