Power Dissipation in Switching Regulator

There are many things that cause power loss.
When current passes through a diode, one form of loss is the Voltage Forward of the diode X Current in the diode. (0.65V X 2A)
When current passes through a MOSFET, one type of loss is "Resistance Drain-Source on" & the current D-S causes loss.
There is power loss because of resistance in the Printed Circuit Board.
Then there is "switching" losses. As the MOSFET turns on/off there is a very short period of time where there is "AC" loss.
The IC needs power to work. That power is lost.

astead hernsley

Also, I don't know what sort of device you're working with, but your datasheet should give you some insight.
I'm not working with a data sheet at the moment. But there is something to be said for data sheets that do provide some calculations. Very helpful when they happen to come with the product.