Is it actually possible to calculate all pokemon stats from just the basics - species, current stats, level, nature?

Question

I'm looking for a reliable stat calculator which actually works. For example, one of the few I tried out said my pokemon(singular not plural) had an overall score of above 700 which isn't possible.
Further more with the caculation methods sometimes the stats would decrease as I increase the level.

e.g at level 60 it has 182 attack
at predicted lv 61 it has 163 attack

an error is it not???
it may just be the specific calculator though, could anyone suggest a reliable calculator?

also I'm try to calculate the IV's of my pokemon and the calculator often says

does not compute
Speed (153) should be 127 to 146.
The Effort Points or Nature may be inaccurate.

even though I'm certain they are accurate

Answer 1

There are only two formulas for calculating a pokemon's stats:

Hp
____

HP= (( IV+ Base+ (√(EV)/8)xLevel )/50)+10

Variables:

IV-Individual Values
Base-Base Stat for pokemon
EV-effort values, up to 256 (but only get points for up to 252)
Level-Pokemon's current level
_____
All other stats:

S=(( IV+ Base+ (√(EV)/8)xLevel )/50)+5

Same variables for the previous one.

You can use this site to see the pokemon's base stats and things of that nature.