This is the formula to calculate a pokemon's Stats except HP.
The IV, EVs, and nature would stay constant if the pokemon evolves (not including the ones it would gain if it levels up, but this is just for the sake of simplicity.) The base stat would change upon evolving though. Since this changes, the pokemon's stats will as well. Most of the time it is an increase, which is why your pokemon's stats usually jump up more than usual when they evolve.