Expense Ratio
Also called: TER, total expense ratio, fund fees, OCF
The expense ratio is the annual percentage a fund deducts from assets to cover its costs, taken silently from returns rather than billed. The gap between 0.03% and 1% sounds trivial and is not: on $100,000 over 30 years at 7%, it's roughly $180,000 of final wealth. Because fees are the one variable you can predict with certainty, minimising them is the highest-confidence decision available to an investor.
Formula
Annual cost = Expense ratio × Amount invested