0% fees on KCEX spot doesn't mean a free fill

KCEX spot runs 0% maker and 0% taker, and that's real. A new KCEX guide makes the point that it only removes one line from your execution cost. Spread, market impact and the cost of not getting filled are still there, and on bigger orders they're the whole bill.

The image is a live, logged-out capture of the KCEX BTC/USDT spot screen taken this morning: the chart, the full order book with size at each level, and the order panel showing Maker 0% / Taker 0%. Nothing about any account is visible.

What a bad fill costs, in dollars

The guide measures it against the mid price at the moment you decided to trade. On a $50,000 order:

• 5 bps off = $25
• 20 bps off = $100
• 75 bps off = $375

Spread alone

Bid 99.90, ask 100.10, mid 100.00. The spread is 20 bps, and a market buy pays 10 bps over mid just by crossing it.

Walking the book

Say the asks are 20 units at 100.00, 30 at 100.10 and 50 at 100.30. A 60-unit market buy takes the first two levels and 10 from the third: $6,006 total, average 100.10. The top of book looked like 100.00. Size is what moved the price.

Where iceberg orders fit

An iceberg shows only a slice of a larger order and refills it as it trades, so the book doesn't see your full size. The guide is careful: it explains the technique and compares it with TWAP (spread over time) and VWAP (spread with volume), but it does not say KCEX offers a built-in iceberg type, so check the order panel before assuming you can place one. Splitting by hand works on the same idea.

The trade-off is fill risk. Their example: you plan to buy 100 units at $100, only 60 fill, and price runs to $102. The 40 you missed now cost $80 more. Being too patient is a cost too.

Measuring it yourself

Log the mid at decision time, your average fill, how much you planned versus got, and where price went in the minutes after each fill. If price keeps moving against you right after you fill, you're being picked off. Watch your participation rate too: the bigger your slice relative to traded volume, the more you move the market. API users should also budget for latency and partial fills.