What is Slippage?
Slippage is the difference between the expected price of a trade and the price at which it actually executes. It arises when an order consumes multiple levels of the order book, so larger orders and thinner liquidity produce worse average fill prices than the quoted top-of-book price.
Slippage occurs because the quoted price — the best bid or best ask at the top of the order book — represents only the volume available at that single level. A market (taker) order large enough to exhaust that level walks deeper into the book, filling against progressively worse-priced resting orders. The average execution price therefore drifts away from the top-of-book quote, and that drift is slippage. The thinner the book and the larger the order, the wider the gap.
Slippage is distinct from the taker fee, which is a separate percentage charged on notional. Together, slippage plus fees form the round-trip execution cost of entering and exiting a position. On a delta-neutral funding trade you pay this cost twice per leg — once to open and once to close — across two exchanges, so four fills in total each carry their own slippage.
For funding-rate arbitrage this is decisive. The strategy captures a small recurring funding payment (often a fraction of a percent per interval), so the entire edge can be erased if the price impact of getting in and out exceeds the funding you collect over your holding period. A 12% APR funding spread that takes weeks to accrue is worthless if opening and closing the pair costs 1.5% in slippage and fees up front.
This is why a realistic screener models slippage from the live order book rather than assuming top-of-book fills. Walking the actual book for your intended position size, on both the long and short venue, reveals whether a headline funding spread survives execution — or whether it only exists on paper for a $100 order and collapses at $50,000.
Slippage percentage (per fill)
slippagePct = (avgFillPrice − quotedPrice) / quotedPrice × 100 avgFillPrice = Σ(levelPrice × levelQtyFilled) / totalQtyFilled
Sign convention: a buy that fills above the quote and a sell that fills below it both represent positive cost. Round-trip cost ≈ entry slippage + exit slippage + taker fees on every fill.
Buying $50,000 of BTC into a thin ask side
- •Quoted best ask: $60,000.00
- •Fill: 0.50 BTC @ $60,000, 0.20 BTC @ $60,030, 0.13333 BTC @ $60,075
- •Total: 0.83333 BTC for $50,000 notional
- •avgFillPrice = $50,000 / 0.83333 = $60,000.6
- •Wait — recompute with book: 0.5×60000 + 0.2×60030 + 0.13333×60075 = 30000 + 12006 + 8010 = $50,016 for 0.83333 BTC
- •avgFillPrice = $50,016 / 0.83333 = $60,019.2
- •Slippage = (60,019.2 − 60,000) / 60,000 × 100 = 0.032%
- •On a round trip (in + out) plus ~0.05% taker fee per fill, this pair costs ≈ 0.16% — which must be earned back by funding before the trade is profitable.
Slippage vs taker fee
| Slippage | Taker fee | |
|---|---|---|
| Cause | Order walks past top-of-book depth | Exchange charge on notional |
| Depends on order size | Yes — grows with size | No — flat percentage |
| Depends on book depth | Yes — worse on thin books | No |
| Known before trading | Estimated from live book | Fixed and published |
| Applies per fill | Yes | Yes |
FAQ
What causes slippage on a perpetual futures trade?
Slippage happens when your order is larger than the liquidity resting at the best price, forcing it to fill against deeper, worse-priced levels of the order book. The result is an average execution price different from the quote you saw. Thin books and large orders both widen it.
How does slippage affect funding-rate arbitrage?
Funding arbitrage earns a small recurring payment, so slippage on entry and exit can consume the whole edge. Because a delta-neutral trade opens and closes two legs, you pay slippage four times, and a spread that looks profitable can be net-negative after execution cost.
How can I estimate slippage before trading?
Walk the live order book for your intended size: sum the price × quantity at each level you would consume, divide by total quantity to get the average fill price, and compare it to the top-of-book quote. A screener that models this from real depth shows realistic cost instead of an idealized top-of-book fill.
Is slippage the same as the bid-ask spread?
No. The spread is the gap between best bid and best ask at the top of the book; slippage is the additional price movement your order causes by consuming depth beyond that top level. A wide spread and a thin book each worsen your effective cost, but they are separate effects.
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