Tax Years That Are Supported By the Tax Planner
Because the U.S. tax code changes constantly, the Quicken Tax Planner supports two years of tax calculations: the year that the Quicken version was released plus the following year.
For example, Quicken 2018 was released in 2017, so its Tax Planner supports calculations for tax years 2017 and 2018. If you use that version's Tax Planner in 2018, Quicken displays your current (2018) data, but it will continue to use the tax calculations based on the 2017 IRS tax tables.
Keep in mind that Quicken's Tax Planner is not intended as a tax-calculation tool; instead, the purpose of the Planner is to give you a "snapshot" of your tax situation throughout the year.
Using the previous example, if you wanted to view your 2017 data in Quicken instead of 2018, click on the link for "year" in the top left and change it to 2017.