after the Big bang, with the introduction of the skill "HP Boost", the HP you see in the red bar is no longer your true HP, your true HP is actually passively boosted by 20% due to said skill, and this is what shows in the HP window

Now, Hyper body increases your HP by 1.6 of your base+static increases HP what does that mean? any increase that is not a %increase, will be factored when calculating how much HP you will gain from using hyper body, that +500HP ring? yup, it gets increased by 1.6, that 9%HP potential skill from the same earrings? nope.

speaking of potentials, potentials that give %HP are NOT counted when doing the HB calculation, however, potentials that increase a fixed amount of HP do count and increase the amount of HP you get from Hyper Body

to calculate how much HP you have without %HP equips, you follow a simple formula, sum all your %HP from equips (so say, i have 9% HP earrings and 6%HP top, that gives a total of 15%HP increase) and then put said number replacing X in the following equation

(100*Current HP)/(120+X)
previous formula is basic rule of three, we use 120 because HP increase is already maxed, in case it was not maxed, the formula would just put the %hp it increases as the last 2 digits, so if it increases 14%HP currently, the number at the bottom would be "114", this is important if you are, say, a mage wondering if you can survive a zakum attack with HB, since mages have no %HP increase skill, it would be simply (100+X) at the bottom

again, the previous formula gives you your base HP + all the static increases to hp, which is what is multiplied by HB, now, there are 2 formulas you can use, one is to determine how much HP HB increases, and the other is to determine what will be your total HP after HB, in order, the formula's are:
(StaticHP*1.60) - StaticHP
this will tell you how much HP you gain from using Hyper Body, then you can simply add that number to your current HP, and that's how much you would have, however, if you want a single formula you can simply punch in a scientific calculator to determine your new HP, here is:

[100*CurrentHP/(120 + X)]*(100 + X + 60)/100

that one is assumming you have the 20% HP increase and everything, X still standing for the amount of %HPincrease from equips you have. however, if you want the really long formula that works with all classes, here is, what each letter stands for after it:

[100*A/(100+B+X)]*(100+B+C+X)/100
long and complicated isn't it, but anways, the letters stand for:
A Current Total HP: gotten from the status window
BPassive Skill %HP increase: the %of HP your passive skills increase (if it is 10%, put 10, if 20%, put 20, etc)
CActive Skill %HP increase: %HP increased by the skill you are using (level 15 HB giving 30%, maxed giving 60%, etc.)
X %HP increase from Equips: basically, the sum of all the %HP increase potentials you have goes here.

Example: i have 20 000HP right now and am going to activate HB, equipped potential equips that give 80%HP total, and the new skill HP Boost maxed (20% HP), so is HB (60%)
Formula goes:
[100*A/(100+B+X)]*(100+B+C+X)/100

[100*20 000/(100 + 20 + 80)]*(100 + 20 + 60 + 80)/100
[2 000 000/200]*(260/100)
10000*260/100
2 600 000/100
26000 that would be your HP after HB, as you can see, nowhere near 60% of the 20k we started with. [PROVEN]