Network Congestion: Why the Whole Chain Slows Down When Everyone Shows Up at Once
What's actually happening when a network gets congested, why it isn't a bug, and the specific approaches different blockchains take to cope with it.
By Firoz Khan|19 September 2026|Updated 11 October 2026|3 min read
Network congestion happens when the number of people trying to transact exceeds the amount of block space available to process them, and it's a direct, structural consequence of a deliberate design choice, not a technical failure that needs fixing outright.
Why block space is limited in the first place
Blocks are deliberately capped in size, partly to keep the amount of data every node has to store and verify manageable, which is what keeps the network genuinely decentralised, a network only ordinary hardware can help validate stays far more open than one that requires industrial-scale infrastructure just to participate.
What congestion actually looks like in practice
Pending transactions pile up in the mempool waiting for inclusion, gas fees spike as people bid against each other for the limited space available in the next block, and confirmation times stretch out noticeably, sometimes from seconds to many minutes on a genuinely busy network.
On Ethereum, the base fee is set by an algorithm and adjusts with demand. You pay at least the base fee for your transaction to be valid, plus a tip if you want validators to prefer it, and the base fee is burned. When blocks are full, the base fee rises. When they are not, it falls. Say a swap uses 150,000 units of gas, and demand doubles the base fee from 30 to 60 gwei. The cost roughly doubles, from about 0.0045 ETH to about 0.009 ETH before tips. The figures are an example.
How Ethereum's fee mechanism responds
According to ethereum.org, each block has a target size, with a maximum of twice the target. When blocks run above target the base fee rises, and when they run below it the base fee falls, by at most 12.5% from one block to the next. The base fee is burned, and a separate tip goes to validators to prefer your transaction.
The page gives a worked example. A simple transfer uses 21,000 units of gas. With a base fee of 10 gwei and a tip of 2 gwei, the cost is 21,000 × 12 gwei, which is 252,000 gwei or 0.000252 ETH. If you set a maximum fee above what is needed, the difference is refunded. If a transaction runs out of gas part-way, its changes are reverted but the gas supplied is still consumed.
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What triggers it most often
A popular NFT mint, a major token launch, or a sharp market move that triggers a wave of simultaneous trading are the classic congestion triggers, concentrated demand hitting the network all at once rather than steady, spread-out usage.
How the ecosystem has actually responded
Layer-2 networks absorb a large share of transaction demand off the congested main chain. Some newer layer-1 blockchains have been designed from the ground up for much higher raw throughput, trading off some decentralisation for capacity. And ongoing protocol upgrades on established chains, including Ethereum's, have specifically targeted increasing usable capacity over time without abandoning the decentralisation the block-size cap protects.
Ethereum's own upgrades have targeted this. The Pectra upgrade in May 2025 raised the target number of blobs per block from 3 to 6 and the maximum from 6 to 9, increasing capacity for rollups, and ethereum.org says the Fusaka upgrade in December 2025 introduced PeerDAS, a more efficient way for layer-2 networks to post and retrieve data. Ethereum.org's live figures in September 2026 put the average transaction cost at about $0.12 on the main network and about $0.0015 on layer-2 networks.
For a UK user, congestion has a tax angle. A fee paid in crypto is spending that crypto on a service, and HMRC lists transaction fees for inclusion on the ledger among allowable costs for Capital Gains Tax, so keep a record of fees paid, with the date and value in pounds. The FCA says crypto is largely unregulated in the UK and that you should be prepared to lose all the money you put in.
Practical ways to avoid overpaying
- Check the fee estimate in your wallet before confirming, and compare it with the same action at a quieter time of day.
- Set a maximum fee rather than accepting the highest suggestion, if your wallet lets you.
- Ask whether a layer-2 network supports the same action, since fees there are typically a fraction of the main chain's.
- Avoid paying for speed you do not need. A transaction that is not urgent can wait for the base fee to fall.
Where to read more
- Gas fees explained: the full guide to what you are paying for
- Layer-2 blockchains explained: the main route around high fees
- Bitcoin's block reward, size and time explained: why Bitcoin's capacity is fixed
- Crypto taxes in the UK: how fees count in your records
A reminder
The FCA risk warning still applies to higher-risk crypto content. Always assess how much risk you are willing to take before buying.
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