People make an entire career of calculating tax provisions.
You are missing the 2019 Provision amount. In it's most simple form:
+ favorable/unfavorable temps/perms (GAAP to Stat or Stat to tax)
(utilize NOL if available)
x tax rate = current provision.
Also need to include 2018 return to provision (true up 2018 provision amount to 2018 return filed) and there is also a deferred aspect of the provision for DTA/DTLs as well as tax adjustments for things like FIN48.