Most retail traders stop at delta and gamma. Institutional desks live one floor up — in the world of vanna (the sensitivity of delta to implied volatility) and charm (the sensitivity of delta to time decay). These second-order greeks drive enormous mechanical flows around OPEX week and Fed days. Understanding them is the gap between "the market is weird today" and "the market is doing exactly what the dealer book says it should."
Vanna — the delta-IV bridge
Vanna measures how much an option's delta changes when implied volatility changes. For a call OTM by 5%, a 1-point drop in IV causes the option's delta to fall — even with spot perfectly flat. The dealer who is short that call sees their delta exposure shift and has to buy shares to stay hedged.
Multiply by every OTM call across the chain and you get the vanna flow: every time IV drops, dealers buy stock. Every time IV rises, dealers sell stock. That's why "IV crush" days drift upward even when there's no obvious news — it's not "people buying the dip," it's market-makers re-hedging.
Charm — the time-decay hedging engine
Charm is delta's sensitivity to time. As an option approaches expiration, OTM delta decays toward zero and ITM delta migrates toward 1.00. For a dealer who is short OTM calls, that decay means their negative delta exposure shrinks daily even with no spot move at all — and they sell shares to rebalance. That sell flow is small per day but cumulative; across thousands of strikes it's a real bid-removal force into Fridays.
The OPEX week pattern
OPEX week is the third Friday of the month, when quarterly and monthly contracts expire together. Here's why it produces a recurring pattern:
- Mon–Wed: Charm sells dominate. Dealers who are short OTM options shed long-stock hedges as charm pulls deltas toward zero. Tape drifts down on light volume.
- Thu: Vanna kicks in. If IV holds bid into the close, dealers stay flat. If IV drops (the typical case), dealers buy. This is the OPEX Thursday "afternoon rip" that confuses chart-only traders.
- Fri: Pin to the largest-OI strike. With expiration gamma maxed out, dealers hedge aggressively at the nearest strike, mechanically pinning spot.
- Mon (post-OPEX): Position reset. The expired OI is gone; new OI starts building at far-OTM strikes. Vanna/charm flow drops to zero for a few days, and macro flow can drive the tape again.
Fed days and the vanna bid
The 24 hours before a Fed announcement is the cleanest vanna setup of the month. IV is elevated heading in. As Powell speaks and IV starts to fall (regardless of whether he's hawkish or dovish), dealers who are short upside gamma have to buy shares to re-hedge. This is the "post-Fed bid" — it's not optimism, it's vanna covering.
The trade: long SPX into the IV crush, not as a directional bet but as a vanna structural bet. Out by close.
Reading vanna and charm on a chain
VEX (Vanna Exposure) is computed the same way as GEX — gamma × OI × multiplier — but with vanna substituted. Strikes with the largest VEX values are where IV moves will translate to the biggest dealer rehedge flows. CHEX (Charm Exposure) does the same for charm.
The institutional read is to look at the distance from spot to the largest VEX and CHEX walls. When they're aligned with the gamma walls (4-way confluence), the level is fortified by every greek's hedging flow at once.
On GEXRadar's Greeks chart, you can switch between GEX / DEX / VEX / CHEX views to see each greek's wall structure independently. The Confluence tab on the Major Walls panel highlights strikes where multiple greeks stack on the same level.
The practical playbook
- Don't trade against the vanna direction on Fed days. The flow is mechanical and predictable.
- Expect a charm-driven low on OPEX Wednesday/Thursday morning, with a vanna-driven recovery into the close.
- The post-OPEX Monday is the cleanest macro day of the month — vanna and charm are quiet, and your directional bias can actually run.
- Big VEX walls predict where IV moves will produce the largest mechanical buying or selling. Use them as targets, not signals.