Although you might start making money soon it can take more than one year to be able to consistently go above the $3k per month. Also, in the beginning you might need to put some money in the business like buying new computers, new cellphone, costs of creating a company... Last but not least you should have an emergency fund for unexpected events and to able to find a job again if in need.

Of course this is not science, but I think most entrepreneurs (including me) are overoptimistic about the time it takes to reach certain goals.