25-Delta Skew as a Positioning Signal
The shape of skew is set by who is hedging and who is selling. Reading it carefully tells you what positioning looks like before any survey or report would.
The 25-delta risk reversal
The 25-delta risk reversal is the IV of the 25-delta put minus the IV of the 25-delta call. Both options are equidistant in delta terms from at-the-money. If the put has higher IV than the call, the risk reversal is positive. If the call is more expensive (in IV terms) than the put, it is negative.
For SPX, the 25-delta risk reversal is almost always positive. Put protection is structurally bid relative to call exposure. The size of the positive number tells you how much.
What changes the skew
Skew steepens (risk reversal goes up) when demand for puts rises faster than demand for calls. This happens during selloffs, before known risk events, and when institutional hedging programs are active.
Skew flattens (risk reversal goes down) when call demand rises (often during melt-up rallies and squeeze conditions) or when put demand falls (often during long calm periods when complacency builds). A flattening skew can signal that positioning has rotated from defensive to offensive, which is itself a contrarian indicator.
Skew as a positioning gauge
Most positioning data (CFTC commitment of traders, prime broker reports, etc.) is published with a lag and incomplete coverage. Skew is calculated from live options markets and reflects positioning in real time.
When SPX skew is at the high end of its range, it usually means hedging programs are actively buying puts. This implies institutional positioning is defensive. When skew is at the low end, hedging demand has dried up, often coinciding with complacent positioning.
Both extremes have predictive content. Very steep skew often precedes mean reversion lower (the hedging demand is already in price; further panic is unlikely). Very flat skew often precedes a vol expansion (the lack of hedging means the next selloff finds nobody covered).
Skew vs ATM IV
Skew and ATM IV can move independently. ATM IV measures the level of the vol surface; skew measures its shape. Three combinations are common:
- High IV, high skew: classic stress. Both hedging demand and overall vol expectations are elevated.
- Low IV, high skew: ambient calm with persistent tail-risk hedging. Often seen in late-cycle markets where overall vol is suppressed but smart money is paying for protection.
- High IV, low skew: vol expansion driven by realized chop, not by directional fear. Often seen in choppy ranges with no clear trend.
The combinations matter. Selling vol when IV is high but skew is flat is a different trade than selling vol when both are high. The skew structure tells you what is driving the IV.
Other skew measures
Beyond the 25-delta risk reversal, traders watch:
- 10-delta vs 25-delta skew: the curvature of the wing. Steep wing skew indicates demand for far-OTM tail protection.
- SKEW Index (CBOE): a single number that captures the slope of the SPX vol surface. Higher = more wing premium.
- Put-call IV ratio: a simpler version of the risk reversal that some platforms display directly.
The 25-delta risk reversal remains the most-cited measure because it is liquid (25-delta options are commonly traded), interpretable (a single vol-point spread), and stable (the methodology has not changed in decades).
Skew as a trade
You can trade skew directly. Selling a put spread and using the proceeds to buy a call spread is a long-skew trade (you are short OTM puts, long OTM calls). Doing the opposite is a short-skew trade. Both are vega-neutral first-order but have meaningful skew exposure.
Skew trading is one of the more sophisticated areas of options strategy. The position depends on the second derivative of the vol surface (curvature) and exposes you to skew-of-skew dynamics. Most retail trading does not get here. Institutional vol funds spend a lot of time here.
Vanna risk
Skew positioning has hidden vanna risk. Vanna (L.09) is the change in delta when IV changes. Steep skew means high vanna. If IV drops sharply (often the case after a stress period passes), the vanna of dealer positioning can release substantial buying pressure into the market.
This is why post-stress SPX rallies are often more violent than the initial selloff. Once the storm passes, dealer covering of put hedges (released by vanna and charm) compounds with general buying interest. The mechanism is mostly mechanical, not sentiment-driven.
What you carry forward
- The 25-delta risk reversal is the IV of 25-delta puts minus 25-delta calls.
- For SPX it is structurally positive; the size of the number signals positioning.
- Steep skew indicates active hedging; flat skew indicates complacency.
- Both extremes have predictive content for vol direction.
- Trading skew directly is a sophisticated area requiring careful Greek management.