Start with the evidence
Gather the source amount, documented rate calculation and separately stated fee. Avoid inferring a fee from a mismatch when the source does not identify one.
Work through the example
A fictional EUR100 conversion at USD1.10 produces USD110. A separately documented USD2 fee makes the combined outflow USD112. The calculation is clear because each component has a defined role.
Make the next step clear
Retain the fee source and let the responsible reviewer determine treatment. If the components do not reconcile, preserve the difference instead of adjusting the rate to make it disappear.
Keep the source context
All exchange rates in these worked examples are fictional arithmetic inputs, not current market rates. A business must use the source, date and method appropriate to its own review and approved accounting process. Keep original currency amounts available throughout.