How does a pokemon's IV change their overall stats?
Say I have Vaporeon with 15/15/10 Att/Def/Stam. How big of a difference will the 10/15 HP stat be compared to one with 15/15 HP?
Will it be the difference of 3-5hp or 10? Since every stat counts I want to know how much or little of impact it will have on end play.
Answers
The influence of IVs on CP value will depend on the base stats of your Pokemon, but the influence of stamina IV on HP is only dependent on the level of the Pokemon - species and base stamina do not make any difference.
15 stamina IV on a Dragonite gives the same nominal HP increase as 15 stamina on a Magikarp, as long as they are the same level, and that is simply the stamina IV multiplied by your Pokemon's CPM value (which is based on it's level), which you can find here:
https://pokemongo.gamepress.gg/cp-multiplier
So for example, 15 stamina IV results in 12 more HP at level 40 compared to 0 IV, since 15 x 0.79 = 11.85 which gets rounded to 12.
To figure out the difference between 10 and 15 stamina IV, just take the difference (5) and multiply it by the CPM value. So for example a level 30 Pokemon with 10 stamina IV would have 3-4 less HP than a Pokemon with 15 stamina IV, depending on how rounding works on stamina - I don't know if it always rounds up or not (5 x 0.7317 = 3.6585).
The CP calculator on this site can help you find the difference in CP / HP of Pokemon with different IVs, just enter the species of Pokemon and enter the IVs that you want to find the values for, here:
https://pokemongo.gamepress.gg/cpcalc#/
For actual combat effectiveness, IVs do not always make a difference to the damage that you deal or receive, since damage values are rounded down.
As an example, If your damage with 0 IVs would be 5 and it would thereotically be increased by 10% to 5.5 damage, it still gets rounded down back to 5, however damage dealt also depends on the defender's stats, so it's possible that your attack IV doesn't make a difference in one scenario where it would in another.
