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Understand US Market Structure and Short Volume
Updated 31 October 2026 · 2 min read · 14 Contents
Plain-language meaning
US Market Structure shows daily off-exchange short-sale volume from FINRA's published short-sale files and expiry-level US listed-options volume, open interest and same-day-expiry activity.
Why it is useful #
It helps a researcher read daily short-sale volume correctly — as trade activity, not outstanding short interest — and see where options activity is concentrated by expiry.
Where it appears and the workflow #
Open US Market Structure (/Research/UsMarketStructure). Optionally enter a symbol, choose NASDAQ or NYSE and an instrument type (equity, ETF, index or other), and pick a window of 5, 20, 60 or 90 days.
Calculation or source #
FINRA-reported short percentage = FINRA short volume ÷ FINRA reported total volume × 100, from FINRA's daily off-exchange short-sale file. Options rows are expiry-level volume, open interest and same-day-expiry figures from stored listed-options data.
Prerequisites, inputs, period and unit #
Volumes are share or contract counts, and the short percentage is a percentage of FINRA-reported off-exchange volume. Windows count completed trading days.
Worked example #
Illustrative only: 1,200,000 short-sale shares out of 2,500,000 FINRA-reported shares is 48.0%. This reflects market-maker and hedging activity in that volume, not 48% short interest.
What high and low mean #
A higher percentage means a larger share of reported off-exchange volume was marked short, which is common for liquidity provision; it is not a bearish reading.
Positive, negative and zero #
Volumes are never negative. Zero means no reported short sales that day. Missing daily files are unavailable.
Limitations and common mistakes #
Daily short-sale volume includes exempt and hedging trades and does not measure outstanding short interest, which is published separately on a twice-monthly schedule.
Market-specific differences #
US equity trading is fragmented across many exchanges and off-exchange venues; this view covers only FINRA-reported off-exchange volume, not consolidated volume.
Suggested next steps #
Pick one symbol on a 20-day window and record the average short percentage, then explain why it does not equal short interest.
Educational use only #
This guide explains descriptive research evidence. It is not investment advice, a price prediction, a recommendation, a claim of predictive accuracy, or an instruction to buy, sell, rebalance or place an order.