You're watching your perp position. The chart says the price moved in your favor. But your unrealized PnL barely changed. Or the opposite: the chart dipped slightly and your PnL swung harder than expected. You're not going crazy. You're probably looking at the last price while your PnL is being calculated off the mark price. These are two different numbers, and understanding the gap between them is essential for anyone trading perpetual futures.
What Is the Last Price?
The last price is exactly what it sounds like: the price at which the most recent trade on that specific exchange was executed. When someone buys and someone sells, the price they agreed on becomes the last price. It updates with every single trade.
This is the number that moves the candlestick chart. It's the most visible price on any trading screen. And for spot trading, it's basically the only price that matters.
On perpetual futures, though, the last price tells an incomplete story.
What Is the Mark Price?
The mark price is a "fair value" calculation that exchanges use to determine your unrealized PnL and, critically, when your position gets liquidated.
Instead of relying on the last trade that happened on one exchange, the mark price pulls data from spot prices across multiple exchanges and applies a formula to produce a more stable, manipulation-resistant reference price.
The logic: if one exchange's price spikes or dips due to a large order, low liquidity, or manipulation, the mark price doesn't follow that anomaly. It reflects the broader market consensus of where the asset is actually trading.
Why Do Two Prices Exist?
Because relying on a single exchange's last traded price for liquidation would be dangerous.
Imagine someone places a massive market sell order on one exchange, temporarily crashing the price by 3%. On a highly leveraged perp, that 3% flash crash could liquidate thousands of traders. But the "real" price across all other exchanges barely moved — it was just a liquidity event on one platform.
If liquidation was based on the last price, those traders would lose their margin because of a blip that corrected itself in seconds. The mark price prevents this. It smooths out single-exchange anomalies and anchors PnL and liquidation to a more reliable number.
This is a protective mechanism. It makes the system more fair.
How the Mark Price Is Calculated
The exact formula varies by platform, but the general approach is:
Step 1: Take the spot price from multiple major exchanges (often a volume-weighted or median average).
Step 2: Calculate a "fair price" for the perp based on this aggregated spot price plus the current funding rate basis.
Step 3: Smooth the result to prevent sudden jumps.
The result is a price that tracks the broader market closely but doesn't react to every single trade on every single venue. It's more stable than the last price and much harder to manipulate.
How This Affects Your PnL
Your unrealized PnL on a perps position is calculated using the mark price, not the last price. This is why your PnL can seem disconnected from what the chart is showing.
Scenario 1: You're long BTC. The last price on your exchange spikes to $67,000 on a thin wick, but the mark price only moves to $66,200 because spot prices on other exchanges are lower. Your PnL reflects the $66,200 mark price, not the $67,000 wick.
Scenario 2: The last price dips briefly to $64,000 on a flash crash, but the mark price stays at $65,300. Your PnL barely moves, even though the chart showed a sharp drop. The mark price protected you from a fake-out.
Once you close the position, your realized PnL is based on the actual fill price of your closing order. So the mark price governs your unrealized PnL and your liquidation threshold, while the actual trade price governs your final result.
How This Affects Liquidation
This is the part that really matters. Liquidation on virtually every major perps platform is triggered by the mark price, not the last price.
If your liquidation price is $62,000 and the last price on your exchange drops to $61,500 but the mark price stays at $62,300, you're not liquidated. The mark price didn't reach your level.
The reverse is also true, though it's less common: the mark price could reach your liquidation level even if the last price on your specific exchange hasn't quite gotten there, because the broader market (reflected in the mark price) has moved enough.
Always check which price your platform uses for liquidation. Almost all use mark price. But knowing for sure matters when your margin is on the line.
When the Gap Between Mark and Last Price Gets Wide
Usually, the mark price and last price are very close — within a few dollars on an asset like BTC. But in certain conditions, the gap can widen:
- High volatility. During rapid moves, the last price can overshoot or undershoot the mark price significantly as aggressive orders push the price beyond fair value.
- Low liquidity. On thinner markets, a single large order can move the last price far from the mark. This is common on smaller altcoin perps.
- Funding rate extremes. When the funding rate is very high or very low, the perp price can trade meaningfully above or below spot, widening the mark-to-last gap.
When you see a wide gap, it's a signal that the local market is temporarily dislocated from the broader one. This can create short-term opportunities — or short-term confusion if you're not watching the right price.
Practical Takeaways
- Watch the mark price for PnL and liquidation. The chart shows last price. Your margin health depends on mark price. Know where each one is.
- Don't panic on wicks. A wick on the last price chart doesn't mean your PnL moved that much. Check the mark price before reacting.
- Set alerts on mark price if possible. Some platforms let you set alerts based on mark price rather than last price. Use them for more accurate risk monitoring.
- Factor this into stop loss placement. Your stop loss triggers on the last price (it's a regular order). Your liquidation triggers on mark price. In fast markets, a wick can trigger your stop even if the mark price didn't move much. Understand this gap when setting stop levels.
Trade Perps on Liquid
- Download the app. Head to tryliquid.xyz and grab Liquid from the App Store or Google Play.
- Create your account. Sign up with email or connect a wallet. On-chain, self-custody.
- Deposit USDC or USDT. No waiting. No delays.
- Trade with clarity. See mark price and PnL in real time across BTC, ETH, AAPL, TSLA, and more. 24/7.
- Earn points. Every trade earns points through Liquid's points program.