What is Index Price?
Index price is a reference value for a perpetual contract's underlying asset, computed by aggregating spot prices across several major exchanges. It represents the fair external market price, filtering out any single venue's manipulation or outliers, and serves as the anchor for mark price and funding.
The index price (sometimes called the index or spot index) is a composite spot price for the asset underlying a perpetual futures contract. Rather than trusting any single exchange, a venue aggregates the spot mid-price from several major markets — often with outlier rejection and weighting — to produce one fair external reference. For a BTC perp, the index might blend BTC/USDT spot from Binance, Coinbase, OKX, Kraken and others.
The index price is deliberately independent of the perpetual contract's own order book. This separation is what makes it useful: the perp can trade at a premium or discount to spot (that gap is the basis), but the index stays anchored to the outside world. Because it draws from multiple venues, a wick or spoof on one exchange cannot drag the whole index, which protects traders from manipulation-driven liquidations.
The index feeds two critical mechanisms. First, mark price — used for unrealized PnL and liquidations — is typically derived from the index plus a smoothing or funding-basis component, so liquidations reference fair value, not a thin local book. Second, funding rate calculation compares the perp's average price to the index: when the perp trades above the index, the funding premium is positive and longs pay shorts, pulling the contract back toward spot.
For funding-rate arbitrageurs, the index price is the invisible tether behind every carry trade. Your funding income exists precisely because the perp deviates from its index; funding is the market's mechanism for closing that gap. Since each exchange builds its index from a slightly different basket of spot sources, two venues can report marginally different index (and therefore mark) prices for the same asset — a nuance that matters when you hold a delta-neutral long-on-A / short-on-B position and compare marks, entry basis, and settlement across legs.
Index price for a BTC perp (multi-venue spot blend)
- •Spot BTC/USDT across constituent exchanges:
- • Binance: $61,980 Coinbase: $62,050 OKX: $62,010 Kraken: $61,960
- •Index price = average of accepted sources ≈ $62,000
- •Perp last trade on the venue: $62,124
- •Basis = (62,124 − 62,000) / 62,000 = +0.20% → perp at a premium
- •Funding premium is positive → longs pay shorts, nudging the perp back toward the $62,000 index.
FAQ
What is the difference between index price and mark price?
Index price is the raw fair spot value aggregated from external exchanges. Mark price is derived from the index (often index plus a funding-basis or smoothing term) and is what the venue actually uses for unrealized PnL and liquidation. The index is the input; the mark is the applied output.
How is the index price calculated?
A venue takes the spot price of the underlying from several major exchanges, rejects outliers or unavailable feeds, and averages (sometimes weighting by volume). This multi-source blend produces one fair reference that no single exchange can easily manipulate.
Why does index price matter for funding arbitrage?
Funding rate is calculated from how far the perpetual trades above or below its index. Your carry income is literally the payment for that deviation. Because each exchange builds its index from a different spot basket, marks can differ slightly between your long and short legs — worth checking before entry.
Can the index price differ between exchanges?
Yes. Each venue chooses its own constituent spot markets, weighting, and outlier rules, so index (and the resulting mark) prices for the same asset can differ by a few basis points. This small gap can affect entry basis and settlement on multi-exchange delta-neutral positions.
See index price live across 36 exchanges.
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