Mark vs Index vs Last Price
Three different "prices" on the same screen — and the one you're watching is almost never the one that decides whether you get liquidated. Five minutes that save you from a confused liquidation later.
Open any crypto perpetual exchange and you'll see at least three numbers near the chart, all called some flavor of "price": Last, Mark, and Index. Most beginners assume they're the same thing. They are not. Confusing them is one of the most common reasons traders get liquidated at a price that "shouldn't have happened."
01The three prices, in plain language
| Price | What it is | Used for |
|---|---|---|
| Last | The actual price of the most recent trade on this perp | Drawing the chart you watch |
| Index | Average spot price across major exchanges | Funding calculation · reference truth |
| Mark | A smoothed price (index + small adjustment) | P&L · liquidations · margin checks |
The Last price is what the candles on your chart are made of — it's the price of the very last trade. The Index price is what BTC is actually worth across the major spot exchanges right now. The Mark price is the one the exchange uses internally to decide whether you've been liquidated, and to update your unrealized P&L.
02Why we need three (instead of one)
Best Buy lists a 65-inch OLED at $1,899. Down the road, Walmart has the same model at $1,879. Target's at $1,909. The "real" price is somewhere around $1,895 — the average. Now imagine one store has a single weird trade: a buyer paid $2,400 for an hour because their card glitched. Should that one outlier define the price of the TV? Obviously not. You'd use the average.
That's exactly why exchanges separate Last from Mark. On a leveraged perpetual, a single weird trade — a thin order book, a flash spike, a fat-finger — can push Last hundreds of dollars away from where the asset actually is for a few seconds. If liquidations were tied to Last, every flash wick would trigger a cascade of unfair liquidations.
So the exchange invented Mark: a smoothed price built from Index (spot truth from multiple exchanges) plus a small funding-aware adjustment. Mark is what your margin is actually measured against. A 1-second wick on Last doesn't move Mark.
03What this means in practice
When you open a position, the exchange shows you a liquidation price. That price is measured against Mark, not Last. So:
- Your chart can wick through your liquidation level for a moment and you stay alive — because Mark didn't follow.
- Conversely, if Mark moves to your liquidation level even briefly, you're liquidated — even if Last is "above" that level on your chart.
- Your unrealized P&L on the screen is calculated from Mark, not Last. That's why your P&L sometimes seems off by a few dollars compared to "what the chart shows."
"My chart never touched 60,000 but I got liquidated at 60,000?" — almost always means Mark hit 60,000 while Last was still a few dollars higher (or vice versa during a wick). The chart shows Last. The liquidation engine watches Mark. Both can be right.
04How to actually use this
- Set stops using Mark, not Last, if your exchange offers the option. Most do — it's a checkbox when you place the order. Stops on Last can get blown out by wicks; stops on Mark won't.
- Read the Mark price displayed near the order ticket — that's the one that matters for your survival, not the candle close.
- Don't panic at brief wicks on the chart. If your liquidation price is at 60,000 and the chart wicks to 59,900 for a half-second, check Mark — if Mark stayed at 60,300, you're fine.
- The Index (the spot average) is the "anchor of truth." Watch it during fast moves. If Last is diverging from Index aggressively, the perp is in stress — opportunity or danger, depending on which side you're on.
The chart shows Last. The liquidation engine watches Mark. Mark is built from Index (spot truth). When in doubt — about your stop, your P&L, your liquidation — Mark is the price that decides your fate.