Compare the same market units
Both selected markets quote Bitcoin in US dollars. A BTC/USDT market is not silently substituted because a stablecoin quote introduces another price relationship. The comparison takes the ask on the buy venue and the bid on the sell venue, then reports the gross difference in basis points.
Each venue row includes its displayed quantity and timestamp convention. Coinbase may provide a snapshot time; Kraken's response here is labeled with browser receipt time. Independent REST requests do not create an atomic cross-exchange view.
Size and costs can remove a visible spread
The maximum top-level quantity is the smaller of the buy venue's ask size and the sell venue's bid size. If your input exceeds that amount, the tool refuses to estimate a full fill from the limited data. It also excludes obviously stale or mismatched observations from the after-assumption calculation.
The calculation subtracts a fee on each leg's actual quoted value, plus a separate buffer on the purchase value. It does not include balance transfers, future rebalancing, deeper levels or partial-fill handling. A positive estimate is a conditional snapshot result, not a reserved or risk-free trade.