Why are my 2017 "federal deductions" so much more than 2018?

[AnthonyC]

It's likely because of the tax law reform changes made that took effect this year.

The standard deduction was doubled but many itemized deductions are now limited (state and local income and real estate taxes) or have been eliminated entirely (such as misc deductions like job related expenses).

Also, personal exemptions (which show as deductions in the TurboTax Summary) were eliminated.  Last year, you could claim $4,050 for yourself, spouse, and dependents.  These exemptions were eliminated for 2018.  But, there was a doubling of the Child Tax Credit.