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Charm Exposure (CHEX)

See how time decay shifts dealer deltas. Charm measures the sensitivity of delta to time - as time passes, dealer deltas change automatically, triggering hedging flows even without price or volatility moves.

Charm exposure analysis shows strike-level dealer delta decay. Enter any symbol to see net CHEX, the charm interpretation, and call/put walls - updated with live options data.

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What can you do with CHEX?

Expiration Flows

Charm intensifies as expiration approaches - critical for 0DTE. See which strikes will generate the largest automatic delta shifts as contracts decay.

Time Decay Hedging

See which strikes will trigger the largest dealer hedging from time passing alone - no price or vol move required.

Into-the-Close Bias

Charm flows often accelerate into market close, revealing late-day directional bias. Use CHEX to anticipate end-of-day hedging pressure.

Get this via API

curl 
# Single expiry (free tier)
curl -H "X-Api-Key: YOUR_API_KEY" \
  "https://lab.flashalpha.com/v1/exposure/chex/SPY?expiration=2026-03-07"

# All expirations (Growth+ tier)
curl -H "X-Api-Key: YOUR_API_KEY" \
  "https://lab.flashalpha.com/v1/exposure/chex/SPY"
Python 
import requests

r = requests.get(
    "https://lab.flashalpha.com/v1/exposure/chex/SPY",
    params={"expiration": "2026-03-07"},  # yyyy-MM-dd
    headers={"X-Api-Key": "YOUR_API_KEY"}
)
data = r.json()
print(f"Net CHEX: {data['net_chex']}")
print(f"Interpretation: {data['chex_interpretation']}")
Full API docs → Try in playground →

Get CHEX via API

Single-expiry CHEX is included on the free Starter plan (5 requests/day). Full-chain CHEX across all expirations available on Growth (2,500/day) and Alpha (unlimited).

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How Charm Exposure Is Calculated

Charm (also called delta decay or DdeltaDtime) measures the rate at which an option's delta changes as time passes. For dealers holding large options positions, charm tells us how much their hedging obligation shifts each day purely from the passage of time - no price or volatility move required.

$$\text{Charm} = -\frac{\partial \Delta}{\partial t} = -\frac{\partial^2 V}{\partial S \, \partial t}$$

Where:

  • $\Delta$ is the option's delta (first derivative of price with respect to underlying)
  • $t$ is time to expiration
  • $V$ is the option price, $S$ is the underlying price

Net CHEX and Dealer Positioning

Charm exposure aggregates the charm across all open interest at each strike, weighted by the dealer convention (short calls, long puts):

$$\text{Net CHEX} = \sum_{i} \text{Charm}_{i}^{\text{call}} \times OI_{i}^{\text{call}} - \sum_{i} \text{Charm}_{i}^{\text{put}} \times OI_{i}^{\text{put}}$$

Positive net charm means time decay is pushing dealers to buy the underlying (supporting price). Negative net charm means time decay is pushing dealers to sell (pressuring price lower).

Charm and Expiration

Charm is most powerful near expiration. As $T \to 0$, delta for near-the-money options changes rapidly, and charm spikes. This is why 0DTE options create massive charm flows - the time-decay-driven hedging can dominate intraday price action.

$$\text{Charm}_{\text{call}} = -\phi(d_1)\left[\frac{2(r-q)t - d_2 \sigma\sqrt{t}}{2t\sigma\sqrt{t}}\right]$$

Where $\phi(d_1)$ is the standard normal PDF, $r$ is the risk-free rate, $q$ is the dividend yield, and $\sigma$ is implied volatility.

Why CHEX Matters for Traders

While gamma exposure tells you how dealers hedge when price moves, charm exposure tells you how dealers hedge when nothing happens except time passing. This is critical because:

  • Expiration acceleration - charm flows intensify exponentially as expiration approaches, especially for near-the-money strikes.
  • Into-the-close flows - as the trading day progresses, the effective time to expiration shrinks, causing charm-driven hedging to accelerate into the close.
  • Directional bias without a catalyst - positive charm creates natural buying pressure; negative charm creates natural selling pressure - all from time alone.

Limitations

  • Dealer assumption - CHEX assumes dealers are short calls and long puts. In practice, some OI is inter-dealer or institutional hedging, which may have different sign conventions.
  • OI is T-1 - open interest is reported end-of-day by the OCC and reflects the previous session's close.
  • Model-dependent - charm calculations depend on the pricing model and implied volatility inputs, which can vary across providers.
  • Not a crystal ball - CHEX describes the mechanical time-decay hedging landscape, not future direction. Use it alongside price action, not as a standalone signal.

What Is Charm Exposure (CHEX)?

Charm exposure - or CHEX - measures how dealer delta changes purely as a function of time passing, with all else held equal. Charm (also called “delta decay”) is the rate at which an option’s delta erodes as time-to-expiration decreases. When you aggregate charm across all open contracts at every strike, you get a map of the time-driven hedging flows that dealers must execute each day simply because the calendar moved forward. Unlike gamma (which requires price movement) or vanna (which requires vol changes), charm-driven flows happen automatically, every single trading day.

CHEX reveals a hidden current beneath the market’s surface. Out-of-the-money options steadily lose delta as they approach expiration, which means dealers who hedged those positions must gradually unwind their hedges. In-the-money options see their delta approach 1.00 (calls) or −1.00 (puts), requiring dealers to add to their hedges. The net effect across all strikes creates a predictable, daily flow of shares that dealers must buy or sell - a “charm wind” that systematically pushes prices in a direction determined by the structure of open interest.

Why Charm Exposure Matters Near Expiration

Charm accelerates non-linearly as expiration approaches. An option with 30 days to expiry might lose 0.01 delta per day from charm alone, but that same option with 2 days remaining could lose 0.10 delta per day - a 10x increase. This means the daily hedging flows driven by charm become enormous in the final days before expiration. For heavily-traded names with large open interest concentrated near the money, charm-driven flows in the last 48 hours can amount to billions of dollars in share buying or selling, creating a powerful and predictable directional force.

The expiration-week charm effect is especially important for understanding the “OPEX drift” that quantitative researchers have documented. As options decay, the steady unwinding of hedges tends to produce a directional bias that persists across the week. When net CHEX is positive (dealers losing long delta), they must sell shares daily, creating a headwind. When net CHEX is negative (dealers losing short delta), they must buy shares, creating a tailwind. Monitoring CHEX heading into expiration week lets you anticipate which directional bias the charm wind will impose - and position accordingly before the flow starts.

How to Use the FlashAlpha CHEX Tool

Enter any optionable ticker in the tool above and select an expiration to see the full charm exposure profile by strike. The chart breaks down call charm (positive, green) and put charm (negative, red) at each strike, showing you exactly where time-decay-driven hedging pressure is concentrated. The tool calculates the net charm exposure across all strikes, giving you a single number that represents the daily directional bias from delta decay alone. Compare this to the GEX and VEX profiles to understand whether time, price, and volatility are pushing dealer flows in the same direction or creating opposing forces.

Access the same charm data programmatically through the FlashAlpha Lab API. Build CHEX into your pre-market analysis scripts, options decay models, or systematic OPEX strategies with a simple REST call. Free-tier accounts include single-expiration CHEX queries for any ticker with no credit card required. Growth-tier plans unlock aggregated multi-expiration views, historical CHEX time series for backtesting, and the throughput needed for scanning charm exposure across your entire watchlist.

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