Last year was my first year using it and so am not sure if I need to buy a new addition for the 2018 tax year
Each tax year is a separate TurboTax program.
Go to this TurboTax website for the 2018 desktop CD/Download editions - https://turbotax.intuit.com/personal-taxes/cd-download/
So the download that was done on my 2017 Turbo tax today is probably the 2018 desktop/CD download?
If you purchased the download from the website posted in the answer then Yes it is the 2018 software.If you need the 2017 software you would need to purchase it from this website - <a rel="nofollow" target="_blank" href="https://turbotax.intuit.com/personal-taxes/past-years-products/">https://turbotax.intuit.com/personal-taxes/past-years-products/</a>