Everyone would like a million pound pay rise. Yet there are very few occupations in the world where you could actually be asking for that and it would be realistic. There is no point asking for something and not knowing exactly how much more you want. It is usually best to keep it in percentages (10%, 15%, 20%) etc. Also ask yourself, Is it feasible or unrealistic for the company? This for me tied directly with the questions of worth. For every business there is an expected return on every pound or dollar spent. You need to know if you can deliver this back. It’s called human resources for a reason (hopefully that doesn’t sound too harsh). Do not be un-aware of it. I was taken more seriously because I had an exact figure I wanted and why I wanted it.