Calculating the input current that can be taken by an Operational amplifier
Offset current is just the difference between bias currents on the two inputs and this can be regarded as fairly constant. For non inverting configurations, input current is bias current plus a dc current proportional to input voltage due to non infinite input resistance and, for higher frequencies, there is a noticeable ac current due to non infinitesimal input capacitance usually a few pico farads.

There are also noise currents if you want to consider those.