If you have low basic and high bonus, it would be good to negotiate from a total package point of view.

Lets say I earn $5k a month now and bonus for the last 3 years average at 6 months. I would say I need annually at least $90k + X% increment from job change to be motivated to move.

You should ask their HR whats the average bonus is like in Barcap, and work your fixed monthly from there. Say if its only 1 month average and lets say you want X% to be 20%, then its 1.2X90/13 = $8.3k per month fixed or $100k per annum fixed.

In this case, overall you will be better off. Do not allow HR to just discount your high variable bonuses. You must factor them in and use average 3 years or so to make a credible case that this variable bonus is in a way part of your current package.

Of coz the discussion is fluid, but the principle that you must not be worst off overall and can see a decent jump to join.

What is decent is really up to you, the market conditions, what is and how far are you from market rate, etc.

Just my 2 cents worth. Feel free to comment guys!