Energy charge
This is the core electricity cost based on your consumed units and the residential slab that applies to your connection. It is the first number to verify because every later percentage or surcharge usually sits on top of that base.
GST
GST is a tax layer added after the energy charge. Many people focus only on the unit rate, but the final bill will still move materially once GST is applied, especially at higher usage.
FC surcharge
FC surcharge is usually applied per unit. It looks small when viewed alone, but it still scales with consumption, which means it matters more on heavier monthly usage.
Fuel price adjustment
FPA changes by billing month. It should not be treated like a permanent unit rate. Some months it raises the bill and some months it pulls the total down, which is why the calculator keeps it visible instead of hiding it in one combined number.
Quarterly adjustment, TV fee, duty, and arrears
These are the lines that often create a gap between a simple online estimate and the real payable amount. If your bill includes electricity duty, quarterly tariff adjustment, TV fee, or arrears, they need to be added explicitly.
Why this matters for the calculator
A serious IESCO bill calculator should show these parts separately. If a tool only gives one total number without telling you what was included, it is harder to trust the result when your real bill arrives.