When you place a trade, you usually see a price quoted on your screen. When the trade actually executes, the price you get may be slightly different. That difference is called slippage. It is one of the most common surprises for people new to crypto trading, and it is not a glitch or a hidden fee — it is a natural consequence of how markets match buyers and sellers.
To understand slippage, it helps to understand what a price really is. On most exchanges, trading happens through an order book: a running list of buy orders (bids) and sell orders (asks) at different prices. The "current price" you see is usually just the price of the most recent trade, or the midpoint between the highest bid and the lowest ask. It is a snapshot, not a promise. Behind that number sits a stack of orders of varying sizes.
A market order tells the exchange to buy or sell immediately at whatever prices are available. If you are buying, the exchange fills your order against the cheapest sell orders first. If your order is larger than the amount available at that best price, the rest of your order climbs to the next-cheapest offers, and the next, until it is filled. Your average execution price ends up worse than the price you first saw. That is slippage caused by depth — or rather, by a lack of it.
The second cause is simply time. Crypto markets trade continuously, and prices can move between the moment you click confirm and the moment the trade is matched. On a busy day, or during a news event, other traders may take the orders you were aiming for before your instruction arrives. On blockchains, this delay is longer, because your transaction has to wait to be included in a block.
This brings up decentralized exchanges, where slippage works a little differently. Many of them use automated market makers, where trades happen against a pool of two assets rather than against other people's orders. A formula sets the price based on the ratio of assets in the pool. Every trade changes that ratio, which changes the price. A small trade barely nudges it. A large trade relative to the pool's size moves it noticeably, and the trader absorbs that movement as slippage. This effect is often called price impact, and it is baked into the math rather than caused by competing traders.
Because on-chain trades take time to confirm, most decentralized exchange interfaces ask you to set a slippage tolerance. This is the maximum amount of price movement you are willing to accept before the transaction is cancelled instead of executed. Set the tolerance very tight and your trade may fail repeatedly in a moving market, costing you network fees each time. Set it very loose and you may get filled at a much worse price than you intended. A loose tolerance can also expose you to sandwich attacks, where someone observes your pending transaction, trades ahead of it to push the price against you, and then trades back afterward to capture the difference.
Several factors make slippage larger. Thin liquidity is the biggest one: assets with few active traders have sparse order books and shallow pools. Trade size matters, since a large order relative to available liquidity will always reach deeper into the book. Volatility matters, because prices move faster during turbulent periods. And timing matters, since liquidity tends to be thinner during quiet hours.
Traders have a few standard tools for managing it. A limit order sets the worst price you will accept; it will not fill beyond that, though it may not fill at all. Breaking a large order into smaller pieces spread over time reduces the impact of each individual fill, at the cost of more exposure to price drift. Trading assets and venues with deeper liquidity generally produces tighter results. And checking the estimated price impact that many interfaces display before confirming gives you a preview of what to expect.
Slippage is not always negative, either. Prices can move in your favour between order and execution, giving you a slightly better fill than quoted. It is simply uncertainty, and understanding where it comes from turns it from a mystery into something you can plan around.
This article is for general education only — not financial advice, and nothing here is a recommendation to buy, sell, or hold any asset. Cryptocurrency carries real risk of loss; always do your own research before making a financial decision.
