If you started your business in 2017 but it begins to become active only in 2018, you can deduct up to $5,000 of start-up costs in 2018. However in TurboTax, if you do not state that you started the business in 2018, the Startup costs will not show up as an Expense in the program.
IRS information on Business Expenses:
https://www.irs.gov/publications/p535#en_US_2018_publink1000208939
