The erosion of a daily-reset leveraged or inverse fund's value in a choppy market, caused by compounding percentage moves off a changing base.
The mechanism is that a percentage loss requires a larger percentage gain to recover, and leverage magnifies both legs. Reset the exposure daily and the asymmetry compounds. Decay grows with the square of volatility and with the leverage factor, so a 3x fund in a volatile index bleeds far faster than a 2x fund in a calm one.
This is not a fee or a flaw; it is arithmetic that follows from the daily objective. It is why the prospectus of every such fund warns against holding beyond a day.
Example: an index alternates plus 5% and minus 5% for 20 sessions and ends down 1.2%. A 2x fund alternating plus 10% and minus 10% ends down 4.9%, four times the index loss on an index that barely moved.
Original diagrams for the ideas on this page. Illustrative, not real market data.
Margin and leverage. A $5,000 deposit can control a $100,000 position, which is 20:1 leverage. Because the loss is measured on the full $100,000, a 2.5% move against you halves the deposit and brings a margin call, and a 5% move uses all of it.
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