Buck Converter Inductor current at Steady State
Take a look at figure 6 on that page (I've added the red lines): -

So, when the input supply voltage is constant and the output voltage and load current is constant (i.e. the circuit is operating in &quot;steady state&quot;), the two current changes (during inductor charge and discharge) are equal.

This mode of operation is called continuous conduction mode or CCM in case you didn't know.