Calculating Your Mitigation AC
Here are the bare bones of how TAKP calculates players' mitigation AC, before the softcap is applied. (For the sake of simplicity, this article leaves out bells and whistles like AAs and monk/rogue/beastlord bonuses.) This article pretty near paraphrases a post by Dzarn, a Daybreak developer. The exact numbers are pulled from the last open TAKP source version.
1. Add up the AC from all your items, including your shield.
2. Multiply that by 4/3.
3. Add 35 if you're an iksar.
4. If you're a pure caster, add defense_skill / 2. Otherwise, add defense_skill / 3.
5. Find the raw spell_AC from your typical buffs (shielding, aegolism, etc.) on TAKP allaclone. (Note: do not use spell_AC values from AllaKabor or Lucy or Magelo or in-game display; those are modifications of the raw value.) If you're a pure caster, add spell_AC / 3. Otherwise, add spell_AC / 4.
6. If your agility is over 70, add agility / 20.
The result of this calculation is your pre-softcap mitigation AC. If it exceeds your class's softcap, your effective mitigation AC will be significantly less.