How to Read Open Interest on Polymarket (US 2026)

Official Markets API names openInterest as current open interest. Official Data Guide lists open interest next to volume as a separate market statistic. Official Events API names the same field Open interest. “Current” is the published word: it is the stock still open, not a tape of fills that already printed. Official Glossary does not reprint a definition row labelled Open interest — we will not invent a calculation those US pages do not print.

Official Markets API names volume as total trading volume and names volume24hr as 24-hour volume (plus volume1wk and volume1mo). Those are published history windows: matches that already happened. Current open interest is not one of those windows. A busy 24h stamp can sit next to a smaller outstanding figure, or the other way around. How to read volume is that tape. This page does not reprint it.

Public international Analytics says open interest measures the value currently held in outstanding positions. That is the closest published “still open” sentence we found. Official Website vs App: US residents browse and trade in the Polymarket US app, not on polymarket.com. We could not confirm that outstanding-positions sentence, or a retail “OI $” chip, on the US help we checked. We will not mash the international wording onto the US swipe as a rule. If the ticket and the docs disagree, trust the live screen.

Official Browse Markets: find markets on the home screen; each tile shows the question, the current Yes and No prices, and a resolution date. Official Place a Trade: tap any market to open it. That opened ticket is where you look for an open-interest / outstanding figure if the live screen prints one. Official Browse Markets does not list Open Interest on the tile. We will not invent a home-screen “OI” chip those pages do not print. If the sports desk is hidden where you live, stop.

Official Place a Trade, Official Browse Markets, and Official Glossary do not reprint a retail column or tab labelled “Open Interest,” “OI,” or “Open Int.” on the swipe we checked. We will not invent one. The action is: on that opened ticket, look at the open-interest / outstanding figure that sits with the market if the live app prints it. If the live control is labelled differently — or is missing — use the live screen, then still separate that stamp from volume and from posted size. Official Website vs App: US residents do that in the Polymarket US app.

Official Markets API market-book and BBO stats name openInterest as current open interest. Official Events API names openInterest as Open interest. Official Market Data Stream names open_interest the same way. Official Data Guide lists open interest under market statistics. Those are published field names. Official Place a Trade does not reprint them as an OI chip. We will not paste an API field onto the US swipe as if the retail page printed that menu.

Official Glossary: an open position is the contracts you currently hold. That is your Portfolio row — How to read your Polymarket portfolio. Market openInterest is a market statistic, not your personal clip. Official Glossary also names an open order as a working bid or ask still sitting. Neither row is a retail Open Interest tab, and neither is a live number we reprint.

Official Glossary: size is the number of contracts available to buy or sell at a given price; liquidity is how much of that size is there to trade. Official Liquidity: that clip is resting orders other users left, waiting to be matched. Official market-book stats name qty as quantity available at a price, plus bidDepth and askDepth as how many levels sit on each side. That ladder is the now-book. How to read liquidity and how to read the order book are those pages. This page does not clone them.

Official Markets API names openInterest as current open interest and names liquidity as current market liquidity. Official Data Guide lists open interest with volume under market statistics — not as L2 depth. A fat outstanding figure can sit next to a thin best ask. Official Spreads: you buy at the ask. Official Prices & Market Data: a market order fills at the best available price on the other side if size is there. Read posted size first. Then glance at open interest as the stock still open.

Official Liquidity: leftover size fills the next prices if the best level cannot cover the clip. Official How are Polymarket odds determined?: Polymarket US does not set prices; odds move when the next orders match. Official Market Settlement: a winning contract still settles at $1.00 and a losing contract at $0.00. Current open interest is not a sportsbook hold, not a locked payout, and not the ask you will pay. We do not reprint a live OI or a live ladder.

Official Markets API and Official Events API can name openInterest. Those are field names, not tonight’s NFL tape we quote. Official market-book teaching JSON includes an openInterest field — a docs example, not a live moneyline. Confirm whatever figure is on the ticket after KYC. We will not reprint a dollar OI, a share count, or a “this market has $X outstanding.”

Official Glossary defines size and liquidity. Official Markets API names openInterest as current open interest. Official US retail help does not print “open interest = volume − closes,” a shares-versus-dollars conversion, or a “safe OI” threshold. We will not invent that equation. Public international Analytics names outstanding positions as a value — we flag that sentence; we do not turn it into a US retail formula.

Public international Get open interest documents a /oi data route. Official Website vs App: US residents trade in the Polymarket US app, not on that website. We will not paste that route, a GLOBAL aggregate, or an international SDK call onto the US swipe as if Place a Trade printed a button. If you wanted the tape, that is How to read volume. If you wanted the chart, that is How to read price history.