Estimated tax penalties a nuisance and sometimes unwelcome surprise.
Predicting what we will owe each year before the year is complete can be complicated, and sometimes it can seem unfair to owe penalty on taxes that are not really due yet, however the authority has been granted to to the IRS to make sure we are paying tax obligations throughout the year, which is basically a normal process for most employed individuals.
The estimated tax process is designed to have the same "throughout the year" effect.