Ok since my maths aint great I found this macro thanks to Kyon.
/script DEFAULT_CHAT_FRAME:AddMessage("Need 102.4 combined avoidance. Currently at:",0.8,0.8,1)
/script DEFAULT_CHAT_FRAME:AddMessage(GetDodgeChance()+GetBlockChance()+GetParryChance()+5+(GetCombatRating(CR_DEFENSE_SKILL)*150/355 +
20)*0.04,1,0.5,0)
The macro assumes you have 5/5 Anticipation. Change the + 20 to the amount of defense skill you get from Anticipation instead if you don't have 5/5 Anticipation.
For tanky help there are these two web sites:-
some web siteZoe's web postBoth I found useful:)