Case Study · Charm into OPEX
Free to readThe Quiet Drift — Charm into OPEX
In a calm week before a big monthly expiration, markets often grind gently higher and then release afterward. A lot of that is charm — the hedging flow that the clock alone generates.
Vanna is the dramatic flow — the vol-crush melt-up. Charm is the subtle one: a steady hedging drift driven purely by the passage of time. It shows up most clearly in the calm days leading into a big monthly options expiration.
The setup
Markets carry their heaviest open interest at the monthly (third-Friday) expiration. In a quiet week heading into it, with implied vol low and price range-bound, gamma is doing little — but charm is not. As each day passes, the deltas on that big OI book decay, and dealers re-hedge. In the common positioning, that re-hedging is a gentle, persistent bid: the market grinds up a little each session for no headline reason.
Low vol, range-bound tape. Charm flow builds as time decays the big OI deltas — a quiet, supportive bid each day.
Charm intensifies as time-to-expiry shrinks. The drift can firm into a pin near the heaviest strikes — gamma and charm together.
The expiring open interest rolls off; the charm (and gamma) support that held the tape together is gone. The market is often freer to move — the post-OPEX release.
Illustrative. Into OPEX, charm hedging supplies a steady supportive bid and the tape grinds quietly higher; once the big open interest expires, that support is gone and the market is freer to move. Schematic, not a price chart.
What the charm read showed
The value of the charm profile is timing. It tells you when the supportive flow is strongest (the final days into expiration) and where it's concentrated (the heaviest strikes). That reframes a quiet, grinding tape: it isn't necessarily conviction buying — it can be the clock forcing dealers to bid. And it warns you about the other side of the trade: when that expiration rolls off, the mechanical support disappears, and the post-OPEX window is where pent-up moves often get released.
A calm grind into a big OPEX is often charm, not conviction. Know when the support is strongest and when it expires — because the market is usually freer to move once the open interest that pinned it is gone.
This case study is free. To watch charm build into an expiration: ETFs with ETF Analytics, single stocks with ETF + Equities, full history via Everything.
See plans →Your next step
Open the tool → Case study: the vanna rally, Nov 2020 → Read: trading vanna & charm →Educational content from Nations Indexes. The OPEX-drift and post-expiration-release dynamics described are widely-discussed market patterns; the figure is an illustrative recreation, not a price chart, and nothing here is investment advice.