Mempool and network fees: why your transfer is stuck and how to save

Mempool and network fees: why your transfer is stuck and how to save

You sent coins, and the transfer has been sitting unconfirmed for an hour. Most often this is not a glitch but the mempool: the transaction is waiting its turn.

In this guide, we explain how the transaction queue works, where the fee comes from and how to avoid losing time and money on transfers between exchanges.

What the mempool is in simple terms

The mempool is a waiting room for transactions. Every transfer you send lands here until it is included in a block.

Space in a block is limited. When there are more transactions than fit, they line up in a queue, and those who paid more go first.

How the network fee is formed

In Bitcoin, the fee is calculated not from the transfer amount but from the transaction's size in bytes. A miner looks at the rate - how many satoshis you pay per virtual byte - and puts the most profitable transactions into the block.

In gas-based networks, which include Ethereum, the fee consists of a base fee and a tip to the validator. The base fee rises when blocks are full and falls when the network is free.

Why a transfer gets stuck in the mempool

• the fee was low, and the network suddenly got congested;
• the wallet set the rate based on an old estimate, and the queue moved ahead;
• in gas-based networks, a previous unconfirmed transaction from the same address is pending ahead of it;
• the exchange has already sent the coins but is waiting for the required number of confirmations before crediting them.

From what we see, beginners often confuse the last point with a stuck transaction. The transfer is already in a block; the exchange simply has not counted enough confirmations yet.

How to speed up a stuck transaction

Bitcoin has RBF (replace-by-fee). You resend the same transaction with a higher fee, and miners take the new version.

The second method is CPFP. The recipient spends the unconfirmed coins in a new transaction with a high fee, and the miner picks up both at once.

In gas-based networks, a stuck transaction is replaced with a new one that has the same sequence number (nonce) and a higher gas price. Most wallets do this with a "speed up" button.

We believe a withdrawal from an exchange can almost never be sped up. The transaction is sent by the exchange, and it is the exchange that picks the fee.

When it is cheaper to transfer crypto

Network load changes throughout the day and the week. It is usually cheaper to transfer on weekends and during hours when trading activity in the US and Asia dies down.

In our view, the simplest approach is to check the current rate in a mempool explorer before sending. If the queue is large and the transfer is not urgent, it makes sense to wait.

With exchanges, the situation is different. Many venues charge a fixed withdrawal fee that does not depend on the network load at the moment.

How the mempool affects cross-exchange arbitrage

In arbitrage, transfer time is a risk. While the coins are in transit, the spread may close and the price may reverse.

A hypothetical example

The numbers are hypothetical. The spread between exchanges is 0.8% on a 3,000-dollar trade, which is 24 dollars before costs.

A transfer on a congested network costs 6 dollars and takes 40 minutes. In that time, the spread narrows to 0.3%, and after trading fees almost nothing is left of the trade.

The same trade via a fast network with a one-dollar fee and a transfer of a couple of minutes keeps almost the whole spread.

• choose a network with fast confirmations if both exchanges support it;
• keep balances on both exchanges in advance so you do not have to wait for a transfer;
• check how many confirmations the exchange requires for crediting;
• factor the withdrawal fee into the trade calculation before entry.

Our tools

When a transfer takes time, it is important to see whether the spread holds while the coins are in transit, and for that you need all exchanges in one window. Our arbitrage screener keeps dozens of venues in one window, refreshes quotes every second and shows each gap together with the volume actually behind it. The spread calculator helps you check what survives fees, network costs and slippage at your size. The bot is fully manual. It never connects to your exchange API keys.

To test the tools on a live market, ArbitrageScanner offers one day of free access to the whole ecosystem.

FAQ (Frequently Asked Questions)

1. What is the mempool in crypto?

It is the queue of unconfirmed transactions. A transfer waits in it until a miner or validator includes it in a block.

2. Why is a transaction taking so long to confirm?

Most often because of a low fee on a congested network. Miners and validators include transactions with higher rates in blocks first.

3. How do I speed up a Bitcoin transaction?

With RBF - resending with a higher fee - or with CPFP, where the recipient spends the coins with a high fee.

4. Can I cancel a stuck transaction?

You cannot cancel it directly. In Bitcoin it can be replaced via RBF, and in gas-based networks with a new transaction using the same nonce.

5. When are network fees lower?

Usually on weekends and during hours of low trading activity. Before sending, it is worth checking the current rate in a mempool explorer.

6. Why should an arbitrage trader watch the mempool?

Transfer delays eat the spread. The longer coins travel between exchanges, the higher the risk that the price gap closes.

Conclusion

The mempool is a queue of transactions where those who pay more go first. A stuck transfer usually means a low fee on a congested network, and it can often be sped up with RBF or by replacing the transaction.

For cross-exchange arbitrage, the mempool means time, and time eats the spread. A fast network, balances on both exchanges and the withdrawal fee included in the trade calculation make transfers more predictable.

IMPORTANT! We are software developers. We do not give recommendations or promises of earnings and we do not advise you to invest your money anywhere. Our software is fully manual, all your money stays under your own control. We show examples of how our clients have earned on arbitrage in the past, but we do not advise repeating those actions one to one. Your earnings depend solely on your own actions and on market factors.