Divide 3 percent by 100 to get a rate of increase of 0.03.
Multiply the rate of increase by the original amount to find the amount of the annual increase. For example, if you started with a salary of $48,000, multiply $48,000 by 0.03 to get $1,440. Alternatively, if you wanted to calculate a 3 percent increase in population and you started with 5 million, multiply 5 million by 0.03 to get 150,000.
Add the increase to the original amount to find the new amount. Completing the first example, add $1,440 to $48,000 to find the new salary equals $49,440. Finishing the second example, add 150,000 to 5 million to get 5,150,000 as the new population.