I was trying to remember how Volt gen 2 handled this question, esp. after noting the comment that ICE cycles (Volt ICE cycles too [edit: should have said varies in RPM too for soc, but, Volt ICE does not cycle like Clarity in Volt "Normal" mode]). This is how Volt gen 2 reported EV vs. gas use for each trip as gallons used (see pic, a random google image find, my gen 2 was sold some years back).
Just a note, in another thread, someone mentioned correctly that when running EV, Chevy Volt engine does not come on -except- for low temperature (or, the occasional maintenance run). Of course after battery depletion, or if "Hold" or "Mountain" modes are selected, the engine runs as needed at an RPM as needed. Another random Volt Gen 2 Google Image picture (
https://gm-techlink.com/?p=5633).
The similarity for battery/gas accounting is that on a long drive, beyond EV range, as a plug in hybrid, some part of the Volt trip is also on gas. Also when Volt ICE is running, the engine RPM can vary as related to maintaining battery minimum SOC, or some % soc in mountain mode, (as opposed to speed alone for ICE).
In EV "Normal" mode, the engine -does not- come on by itself related to accelerator pedal demand (other than as noted above, ERDTT (engine running due to [low] temperature) or maintenance). Also, Volt does not have a Clarity like accelerator detent position that causes ICE to come on.
Volt "Hold" is somewhat analogous to Clarity "HV", and "Mountain" different soc gen 1, gen 2, to Clarity "HV charge", "Sport" in Volt only remaps the go pedal, there is no change in available power.
The closest thing to Volt "Normal" EV mode on battery in Clarity is our Econ mode, because Clarity econ mode at least minimizes ICE starts. However, the far more common Clarity ICE cycling, especially as caused by power demand, go pedal detent, climate settings, and factors yet unknown in any mode, is a significant difference between Clarity and Volt.