Post-Only vs Fill-or-Kill — Which Saves You More?

By Tjnakhon Engineering Editorial Team · Reviewed July 2026

Why Compare These?

If you trade futures on KuCoin, you’ve seen the order type dropdown. Post-Only, Fill-or-Kill, Immediate-or-Cancel. Most traders ignore them. That’s a mistake. Post-Only orders can slash your fees by 75% or more. Fill-or-Kill protects you from partial fills that mess up your strategy. But they work differently. And picking the wrong one costs you money. Let’s break down exactly when to use each on KuCoin Futures.

At a Glance

Post-Only Order Deep Dive

A Post-Only order tells KuCoin: “Only place this order if it adds liquidity to the order book.” That means your limit price must be lower than the best ask (for a buy) or higher than the best bid (for a sell). If your order would immediately match an existing order — becoming a taker — it cancels automatically. No partial fills. No surprise fees.

This is how professional traders keep costs low. On KuCoin Futures, maker fees are typically 0.02% while taker fees run 0.06%. Over 100 trades of $10,000 each, Post-Only saves you $400 in fees. That’s real money. And if you’re a high-frequency scalper, the rebate structure can even pay you a small amount per trade.

The downside? Your order might not fill. If the market moves away from your limit price, you’re stuck waiting. And if volatility spikes, your order could cancel dozens of times before finally getting placed. That’s frustrating when you want to catch a fast move.

• ✅ Pro: Drastically reduces trading fees — can save 60-75% per trade
• ❌ Con: Order may never fill during fast markets or tight spreads

Fill-or-Kill (FOK) Order Deep Dive

Fill-or-Kill is the opposite philosophy. You say: “Fill my entire order immediately at this price, or cancel it completely.” No partial fills. No waiting. FOK is ideal when you need a precise position size and can’t tolerate slippage across multiple small fills. Think of it as a binary switch — either you get exactly what you want, or you get nothing.

On KuCoin Futures, FOK orders are typically used for large entries where even a 1% partial fill could throw off your risk management. For example, if you’re opening a $50,000 short and only $40,000 fills, you’re suddenly overexposed. FOK prevents that. But here’s the catch: FOK orders almost always execute as takers. That means you pay the higher taker fee. And in low-liquidity markets, your order might cancel repeatedly, wasting time and potentially missing the move entirely.

And here’s a practical tip: never use FOK for small orders. If you’re trading 0.1 BTC, just use a market order. The fee difference is minimal, and you’ll actually get filled. FOK shines only when size matters.

• ✅ Pro: Guarantees no partial fills — protects your position sizing
• ❌ Con: Always pays taker fees — 3x more expensive than Post-Only

Head-to-Head

Let’s walk through three real scenarios. These are simulated examples based on typical KuCoin Futures market conditions.

Scenario 1: Scalping Bitcoin with 0.2 BTC per trade.
You’re scalping 10-20 point moves on BTC. Your strategy uses limit orders 2-3 ticks above the best bid. Post-Only is perfect here. Each trade saves you ~$1.20 in fees versus a taker order. Over 50 trades a day, that’s $60 saved. FOK would cost you $60 extra daily. Post-Only wins.

Scenario 2: Opening a $100,000 ETH short at market open.
You want to short ETH at $3,500 exactly. The order book shows 50 ETH at $3,500, 30 ETH at $3,501, and 20 ETH at $3,502. A market order would fill partially at each level. A Post-Only order at $3,500 would just cancel — you’d be a taker anyway. FOK is your friend here. It fills the full 28.57 ETH at $3,500 or cancels. You know exactly your entry price.

Scenario 3: Adding to a position during low liquidity (altcoin).
You hold a small altcoin position and want to add 10% more. The spread is wide. Post-Only at the bid might take hours to fill. FOK will likely cancel because there’s not enough volume. Your best bet? Use a regular limit order with Immediate-or-Cancel — or just wait for better liquidity. Neither Post-Only nor FOK works well here.

Which Should You Choose?

Here’s a simple decision framework:

• If you prioritize low fees: Use Post-Only for all limit orders where you’re not in a rush. It’s the default choice for professional scalpers and swing traders.
• If you need exact position size: Use FOK only when the order size is large relative to order book depth — typically 10%+ of the top-level liquidity.
• If you’re unsure: Start with Post-Only. If your orders keep canceling, switch to a regular limit order (not FOK). FOK is a specialist tool, not a daily driver.

One more thing: KuCoin Futures offers a “Reduce-Only” modifier that works with both order types. If you’re closing a position, always check Reduce-Only to avoid accidental long/short confusion.

And remember — no order type guarantees profit. Fees matter, but they’re just one piece of the puzzle. Focus on your strategy first.

Key Takeaways

• Post-Only saves 60-75% in fees vs taker orders on KuCoin Futures
• FOK prevents partial fills but costs 3x more in fees
• Use Post-Only for daily scalping; use FOK only for large, precise entries
• Never use FOK for small orders — market orders are cheaper
• Always check Reduce-Only when closing positions

Risks to Consider

Order types are tools, not guarantees. Post-Only orders can leave you unfilled during volatile moves, causing you to miss the trade entirely. FOK orders can fail repeatedly in thin markets, wasting time and mental energy. Neither protects you from slippage on the underlying asset — if BTC drops 2% while your FOK order is pending, you’re still exposed. Always use stop-losses and position sizing. No order type replaces risk management.

Sources & References

• KuCoin Futures Order Types — Official Documentation
• Investopedia — Post-Only Order Definition
• KuCoin Futures Fee Schedule (Maker/Taker Rates)