The CCA amount is pro-rated based on the number of kilometres you used to earn income. Ex: If you drove the car 10000 kilometres, in total, but only 1000 for employment purposes, you only get 10% of whatever the calculated CCA should be.
If you have just purchased or added the car into Class 10 (30%), it is subject to the half year rule, and so only half of the cost of the car is used to calculate CCA for the year. In subsequent years, the full UCC value will be used.