Omni shows two types of profit and loss: Unrealized PnL (UPnL) on your open positions, and Realized PnL once you close.
PnL and UPNL are calculated from two different prices, which is why the number can shift when you close a trade.
Calculating Unrealized PnL (UPnL)
The UPnL on an open position is calculated from the Mark Price: a smoothed fair-value price derived from the underlying spot price, funding rates, and the OLP's current risk profile. The Mark Price is also what Omni uses for margin requirements and liquidations.
Calculating Realized PnL
When you close a position, the trade executes against the Quoted Price: the price the OLP is willing to fill your order at that moment. The Quoted Price reflects live market conditions, including available liquidity, your trade size, and the current spread, so it will almost always differ from the Mark Price.
Why PnL differs from UPnL
Because UPnL uses the Mark Price and your close uses the Quoted Price, the two won't always match exactly. Even if your UPnL shows a profit, your realized PnL can come in lower once the spread and slippage is applied.
To reduce the gap between PnL and UPnL, use a Limit Order to set the exact Quoted Price you're willing to accept, rather than taking whatever quote is available at market. This gives you full control over your exit price.
For full detail on how these prices interact, see Prices on Omni.