Why the gap between «last» prices misleads you, what to subtract, and what to look at besides the percentage.
An exchange shows you the price of the last trade — and most disappointment in arbitrage is built on it. You cannot buy at the last price: that trade already happened. You buy at the ask and sell at the bid.
The gap between the «last» prices on two exchanges looks lovely and means nothing. The real question is different: how much is left once you have actually got in and out.
What to subtract
- The fee on the buying exchange. Take the taker fee: you are lifting someone else's order, not placing your own.
- The fee on the selling exchange. Taker again, for the same reason.
- The transfer cost, if the coin has to move between venues.
QuickRadar subtracts the first two for you: the table shows the spread already net of taker fees on both legs. That is why the number there is smaller than the «price difference» you could work out by eye — and exactly why you can trust it.
Where the prices come from
What you do · At which price buy on exchange A · the ask on A sell on exchange B · the bid on B
That is what an executable spread means. It is always tighter than the «raw» one, and that is fine: the raw spread is the one that does not exist.
What the percentage does not show
The percentage is not everything. Two things kill a trade after the number has already convinced you:
Order-book depth. A 5% spread on an illiquid contract means you can enter with a couple of hundred dollars. Past that, your own order eats the whole difference.
Deposits and withdrawals. If withdrawals are shut on one of the exchanges, cross-exchange arbitrage turns into holding a position for an open-ended stretch of time. That status sits next to every pair — check it before the trade.
What to do with this
Pick the kind of arbitrage that suits you and watch the live numbers: spot, futures, basis or funding. And to stop living in the table, build a rule in the builder — the notification arrives in Telegram when the spread actually shows up.