When you send Bitcoin, your transaction doesn't go straight to the blockchain. It sits in a waiting room called the mempool until a miner picks it up and includes it in a block. Most of the time, that process is smooth. But during periods of high network activity, the mempool fills up, miners grow selective, and anyone who submitted a low fee suddenly finds their payment stuck for hours or even days. That's a mempool fee spike, and it's one of the most common frustrations for Bitcoin beginners.
Why mempool fee spikes happen
The Bitcoin network processes roughly one block every 10 minutes, and each block has a size limit. Only a fixed amount of transaction data fits per block. When more people are sending Bitcoin than blocks can absorb, a backlog builds up in the mempool.
Miners aren't random about which transactions they pick. They choose the ones paying the highest fee rate, measured in satoshis per virtual byte (sat/vB). When the mempool is congested, the floor price to get included in the next block rises sharply. A fee that would have confirmed your transaction comfortably on a quiet Tuesday can leave it stranded on a busy weekend.
Three situations reliably trigger fee spikes:
- Major price moves, when a surge or crash sends waves of traders rushing to buy or sell
- Large protocol events like a halving, which attracts unusual network attention
- Ordinals or other on-chain activity that consumes block space in bulk
How to check the mempool before you send
Sending Bitcoin without checking the mempool first is like merging onto a motorway without looking. The fix takes under a minute. Visit mempool.space, which shows the current backlog in real time, the fee rates miners are accepting, and an estimate of how long your transaction will take at different fee levels.
Look at the "recommended fees" section. It gives you three tiers: high priority (next block), medium priority (around 30 minutes), and low priority (one hour or more). In calm conditions, all three sit close together. During a spike, the gap between low and high can be five to ten times wider. That difference in sats adds up quickly if you're sending a significant amount.
Check the mempool at different times of day. Weekday mornings in Asia and late afternoons in North America (US Eastern time) are typically the busiest windows. Sunday evenings in Australia (which overlap with quiet US and European periods) often see lower congestion and cheaper fees.
What to do if your transaction is already stuck
If you sent with a fee that's now too low, you have two tools available, depending on what your wallet supports.
The first is Replace-by-Fee (RBF). If you enabled RBF before broadcasting, you can resubmit the same transaction with a higher fee, and miners will prefer the new version. Not every wallet exposes this option clearly, so it pays to check before you send. McLeod Pacific Investments recommends verifying your wallet's RBF support before any large transfer.
The second is Child-Pays-for-Parent (CPFP). If you're the recipient of a stuck transaction, or you received change from it, you can spend that output with a high fee. Miners will then pick up both transactions together because processing the child earns them the combined fee. It's a less elegant solution than RBF, but it works when RBF isn't an option.
McLeod Pacific Investments covers the mechanics of both approaches in the guide on Bitcoin fee bumping, which explains when each method applies and how to execute it correctly.
Setting the right fee in the first place
Most wallets let you choose between automatic fee estimation and manual entry. Automatic is fine during quiet periods. During a spike, automatic estimates sometimes lag behind real-time conditions by 10 or 15 minutes, which can mean underpaying at exactly the wrong moment.
For any non-urgent send, choose the lowest fee tier that still fits your timeline. If the payment can wait a few hours, low priority will almost always confirm without issue once the spike passes. If it must arrive quickly, pay for high priority. The mistake most beginners make is choosing a middle-ground fee that's too low for the current block but too high to justify waiting it out.
Never use a fee estimator from a different network state than the one you're in. A sat/vB figure that was reasonable an hour ago may already be obsolete during a fast-moving spike.
A note on timing for Australian senders
Australian Bitcoin holders have a natural advantage they rarely use. Because the busiest global trading windows (US afternoons and Asian mornings) fall during Australian overnight hours, sending Bitcoin late at night or in the early hours of the morning often means lower fees and faster confirmations. It's not a guarantee, but patterns are consistent enough to be worth factoring into non-urgent transactions.
McLeod Pacific Investments is a Gold Coast-based registered Digital Currency Exchange Provider. McLeod Pacific Investments helps Australian buyers and sellers understand not just how to transact in Bitcoin, but how to do so cost-effectively. Mempool awareness is part of that foundation, sitting alongside choosing the right wallet, understanding address types, and knowing when to act and when to wait.