Open Interest
Total open option contracts per strike.
Definition
The count of option contracts at a given strike and expiry that are currently held open — not yet closed, exercised, or expired. Published by the OCC after daily clearing settles.
Formula
OI(t) = OI(t−1) + opens − closes − exercises − expirations
Only opening orders (buy-to-open, sell-to-open) grow OI; closes, exercises, and expirations reduce it.
Inputs
exchange EOD datastrikeexpiryoption type
Output
open_interest (contracts)
Interpretation
- High concentration: strike acts as a magnet/wall into expiry.
- Low: thin strike — low dealer hedging footprint.
- Typical: dispersed OI across strikes — no standout level.
API Reference
Endpoint
GET /v1/options/{symbol}/chain
Tier
Basic (also surfaced in /v1/stock/{symbol}/summary)
Response field
open_interest
Why Open Interest Matters for Trading
TL;DR
OI is the positioning map. Every derived metric — GEX, max pain, call/put walls — is built on top of OI weights. Concentrated strikes pin; dispersed strikes don't.
- What it measures
- The standing inventory of open option contracts at each strike and expiry.
- What it signals
- Where dealer gamma, vega, and charm concentrations sit — the terrain that hedging flow must cross.
- Why we measure it
- OI is the foundation for GEX, max pain, and dealer-positioning analytics.
- Who uses it
- Every options trader, dealer-flow modelers, pin-risk managers, weekly/monthly expiration traders.
How to read Open Interest
High concentration
- OI stacked at one or two strikes
- Pin risk into expiry
- Strike acts as support/resistance
- Source of call/put walls
Good for: pin trades, wall fades
Low
- Thin OI at the strike
- No dealer hedging footprint
- Weak support/resistance
- Flow crosses without drag
Good for: clean directional moves
Typical / dispersed
- Balanced OI across strikes
- No standout level
- Dealer hedging smooth
- Trade direction, not levels
Neutral
Rules of thumb
- OI is EOD, stale intraday. Exchanges publish next-day OI after OCC clears. Volume lags less.
- Compare OI to average volume. 5x normal OI at a single strike is a positioning event worth investigating.
- Near expiry, OI drops fast. Weekly OI decays through the week as positions close; use day-over-day ΔOI to read flow.
- OI ≠ dealer position. OI is long AND short combined. Dealer sign inference requires flow/trade-side data.
- Watch the highest-OI strike — it's often the max-pain target into expiry.
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