A 0% fee doesn't buy you depth: the weekend book-walk math from KCEX's spot execution guide

Sunday, quiet chart, 0% fee on the spot pair, so a market order should be free, right? The commission is. The fill isn't, and KCEX's new guide on weekend spot execution spells out where the cost actually hides when the fee line reads zero.

The image is a live, logged-out capture of the KCEX BTC/USDT spot page from this Sunday morning: 15-minute chart, the full order book with sizes at each level, a limit buy panel, and the fee line showing maker 0% and taker 0%. At capture the best ask was 80,327.94 with about 12.3 BTC on it.

What a 0% fee does and doesn't change

KCEX's published spot baseline is 0% maker and 0% taker, subject to pair rules. The guide's point is narrow and worth keeping: zero commission removes one explicit cost. It doesn't add a single coin of liquidity at the prices you can actually hit.

The book-walk example

The guide uses a hypothetical ask side:

• 20 tokens at 100.10
• 30 tokens at 100.25
• 50 tokens at 100.60

A 100-token market buy takes all three levels. Average fill: (20 x 100.10 + 30 x 100.25 + 50 x 100.60) / 100 = 100.395. The screen said 100.10, but only 20 tokens were there. On a thin weekend book, that gap is your real cost, fee or no fee.

Four ways to execute, four trade-offs

• Market order: almost certain to complete, but pays the spread and walks the book
• Passive limit: you control the price, but it may never fill, and when it does it can be because the price is moving against you
• Sliced limits: smaller footprint on the book, but the market can move while you wait
• Post-only: guarantees you're the maker, but can be rejected or sit unfilled

Three numbers that get mixed up

Spread is the gap between best bid and best ask. Slippage is how far your average fill lands from the price when you decided to trade. Price movement is the market going somewhere on its own while you're executing. The guide treats them as separate, and suggests logging the decision price, the midpoint when the order arrives, and your fill-weighted average, all with timestamps.

Weekend habits from the checklist

• Measure the bid-ask spread and the depth within 1% of mid at the time you plan to trade, and compare by weekday and hour, instead of assuming every Saturday is thin
• Size the order against the depth near the top of the book, not against your account balance
• Remember stop orders aren't guaranteed to fill at the trigger price when the book is sparse
• Don't carry the 0% spot fee into futures math; perps have their own fee schedule plus funding

Grading it over a month

Group your trades by pair, weekday, order type and size, then compare average and worst-case shortfall. Include the limit orders that never filled. If you only look at the good fills, the numbers will flatter you every time.