the index price is a spot-derived reference for what the underlying asset is actually worth, usually computed as a weighted average across multiple major spot exchanges. the mark price is a smoothed, manipulation-resistant version of the perp's current price, derived from the index plus a damped premium. liquidations, pnl displays, and risk calculations on most modern perp venues are driven by mark price, not by the last trade. understanding the distinction is how you stop getting confused when your screen shows one number and your liquidation calc uses another.
in plain english
index price is "what btc is really worth right now, averaged across the major spot venues." mark price is "what this perp should be worth based on the index plus a controlled premium." last price is "the price of the most recent trade on this specific perp." all three can be slightly different at any moment.
why both exist
if liquidations used last price, attackers could wick a single trade on a thin perp market and force liquidations across the entire book. mark price prevents that. by anchoring to a multi-source spot index and adding a damped premium, mark price ignores instant wicks and only reacts to sustained moves.
- last price: most recent fill on the perp, can spike on a single thin print.
- index price: average spot price across multiple cex/dex sources.
- mark price: index plus a damped premium, used for risk and pnl.
- fair price: synonym for mark price on some venues.
how each is calculated
index price is typically a volume-weighted or time-weighted average of spot prices from a set of approved exchanges. mark price is the index plus a moving-average premium that captures how far the perp is currently deviating, but smoothed so a single wick cannot dominate. each venue publishes its exact methodology.
how it shows up on uponly.win
uponly routes to avantis on base. avantis uses chainlink and pyth oracles for index price and computes mark price off those feeds plus its own market data. your liquidation on a rip is triggered by mark price, not by the last on-chain trade. this is what prevents a one-block wick from blowing up your position on a normal market move. for the broader picture on how uponly executes, see how uponly was built in one night.
common confusions
people often assume the price they see on tradingview is the same one used by their perp venue. it usually is not. tradingview shows last price from a specific exchange feed. your perp venue uses its own mark price for risk. close enough most of the time, different in moments that matter.
- liquidation triggers off mark price, not last price.
- pnl on screen is usually computed off mark price.
- mark price is smoother than the candle chart, by design.
- index price is the spot reference; mark price is the perp-aware reference.
see also
- liquidation price definition
- funding rate definition
- perpetual future definition
- slippage in perps
- open interest definition
want to see mark price in action? open uponly, take a small rip, and watch the displayed entry, liquidation, and current price. the price defending your position is the mark, not the chart wick.