As I mentioned before, HP IVs are doubled. Here's the IV formula:
HP / 2 + Str + Spr + Def + Spd = 40
For example, a PERFECTLY AVERAGE Yo-kai will have 8 points distributed in every stat - since HP is doubled, it's actually 16. That would look like this:
HP 16 / STR 8 / SPR 8 / DEF 8 / SPD 8
Total points is 40, since you divide HP by 2 for the formula. If this Yo-kai was on your team, at Lv99 he'd have 16 more HP, 8 more STR, 8 more SPR, 8 more DEF, and 8 more SPD than his base stats. Here's another example: my [[Snartle]]! His IV spread is:
HP 24 / STR 9 / SPR 3 / DEF 7 / SPD 9
As you can see, compared to "average", he has terrible Spirit, slightly above average STR and SPD, and great HP. It adds up to 40, because 24/2 = 12, + 9 + 3 + 7 + 9 = 40. It will ALWAYS add up to 40.