I think it is a combination of what you are currently making, what makes it worth it to you to make a change, and your best determination of "market value."

If you' re staying in the same field, in essentially the same job function, or stepping up a level or two, I think the determination can be made fairly simply (though not perhaps "easily"). Particularly if you are satisfied with your current pay, and either don' t feel you' re underpaid, or have done enough research to be pretty certain of local market value for the job. If you' re changing fields, then your personal requirements (what you need to live on) and your best determination of market value become, I think, more critical.

While the "10 to 15%" rule may work for some, it may be moot for others. A 5% increase with better benefits, more flexibility, and a great work environment may be enough for some people to make the change. On the other hand, 25% may not be enough under some conditions (and I can think of some!).

And, yes, I agree with Chet that you can usually come up with some sort of range that is reasonable and expected for your local job market. E.g., when my husband started looking for another job, he was making, let' s call it $WW,000 per year. We would have loved for him to make $YY,000 per year, and it certainly was what we need in order to both pay the bills and save money! But, jobs in his field don' t pay $YY,000 per year unless you' ve been doing exactly the same type of work for a number of years (more than he has) or have been with the same company for a number of years, or have an advanced degree (which he doesn' t have). So, to ask for that amount of money, based on what we need, would have been foolish and taken him out of the running for most jobs. However, his then-current salary was truly under market. We determined that through a combination of salary.com, what similar jobs are paying in this area (per job postings and interviews with other companies), and what recruiters were telling him he "should" be making. All agreed he was underpaid for what he was doing. And, while salary.com is usually on the high side, in his case it wasn' t far off.

In the end, he got a job making $XX,000 per year, which is more than at his other job (for a similar position but with a lower-level title). It ended up being a bit more than 10% more, but with far better benefits at a much lower cost to us. So, together, those things probably added close to 15% to his previous salary. So, it ended up within your parameters, Paul, but we got to it in a very different way than by just adding 10 to 15% to his then-current salary!

I, on the other hand, based my asking range on the salary I was making at my last job in the "real world," which was five years ago. I did not have, and could not get, a good handle on what market value is for my job function--being a part-time professional applying for a job in a totally different business arena. I more or less used your 10 to 15% rule (though my low end was less than 10%, because I was paid pretty well at the last job, and I knew it). I ended up being way high in my number, but as most of you know by my previous posts, I declined the job but got a subsequent offer close enough to my original range that I could accept it. And certainly money was not the overriding deciding factor, as I' ll be making less than in my last job. But it is a realistic salary for these economic times, and for part-time work. Do I think I am worth more? Yes (and my future boss stated as much). Do I care? Not really.