# Open interest

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Canonical: https://novigapi.com/learn/open-interest

Open interest is the number of contracts in a market that have been bought and not yet closed out or settled.

Open interest counts the contracts that are still outstanding. Every contract has a holder on each side, so open interest counts each matched pair once. It rises when two traders open new positions against each other and falls when positions are closed out or settled. Volume tells you how much traded today; open interest tells you how much money is still riding on the outcome. A market with high volume but flat open interest is mostly traders swapping positions.

## How it works

Whether a trade changes open interest depends on whether each side is opening or closing. If both traders open new positions, open interest rises by the trade size. If one opens and the other closes, the position just changes hands and open interest stays flat. If both close, open interest falls. At settlement every contract is paid out and open interest goes to zero.

## Worked example

How trades change open interest

| Trade | Buyer of Yes | Buyer of No | Size | Volume so far | Open interest |
| --- | --- | --- | --- | --- | --- |
| 1 | A opens | B opens | 100 | 100 | 100 |
| 2 | C opens | D opens | 50 | 150 | 150 |
| 3 | E opens | A closes (sells Yes) | 60 | 210 | 150 |
| 4 | B closes (sells No) | C closes (sells Yes) | 40 | 250 | 110 |
| Settlement |  |  |  | 250 | 0 |


After trade 3, A has passed 60 contracts to E, so volume rose but open interest did not. In trade 4, B and C both closed, so open interest fell by 40. Each contract in open interest is a $1 payout owed to one side at settlement, so 110 contracts of open interest means $110 of payouts outstanding.

## On Novig

Novig's public market data carries volume and open interest per market, and every Novig price is quoted per $1 of payout, so open interest converts directly into dollars at risk. Our `/markets` endpoint returns both figures, `/trades` lists the trades behind them, and `/ohlc/daily` gives daily price bars with volume. The live panel beside this page shows Novig's most traded markets and the ones with the most open interest. Novig's free daily CSVs at data.novig.com, which start 3 Aug 2026, include the trade records; we add names and intraday snapshots.

## When it matters

- Conviction: open interest rising alongside a price move means new money is behind the move, not just traders taking profit.
- Liquidity: markets with large open interest tend to have more makers and tighter spreads.
- Settlement risk: large open interest on a player prop raises the stakes of voids and rule questions, such as how a protected market settles.

For a quick read on how expensive a market is to trade, combine open interest with the spread. The [hold calculator](https://novigapi.com/hold-calculator) shows what that spread costs as a hold-equivalent.

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