As the conclusion of that wild pokemons might not always be odd levels u need to spend stardust
Feed it stardust until u know the pokemons level from http://pokemongo.gamepress.gg/power-up-costs
then calculate max cp with this
Max CP = ((Base_Attack + 15) * ((Base_Defense + 15)^0.5 * (Base_Stamina + 15)^0.5 * Total_CP_Multiplier^2) / 10