An on-chain transaction fee, often called a network fee or gas fee, is the small payment you make to have a blockchain process your transaction. It goes to the network that records and confirms the transfer, not to the wallet or exchange you are using. Every time you send crypto or interact with a blockchain, you pay one.
The fee exists because a blockchain has limited space. Each block can only hold so many transactions, and the people who run the network (validators or miners) prioritize the transactions willing to pay more. The fee is what buys your transaction a place in a block.
Why fees change
The main reason a fee goes up or down is congestion. When lots of people are transacting at the same time, they compete for the same limited block space, and fees rise as users offer more to get processed sooner. When the network is quiet, fees fall. The same transfer that costs $0.20 at a calm hour can cost several dollars during a busy period, with no change in the amount being sent.
Most networks also let you choose a priority. Pay a higher fee and your transaction confirms faster. Pay less and it may sit waiting until space frees up. If you are not in a hurry, the lower setting can save money.
The idea of gas
On Ethereum and similar networks, the fee is measured in units of gas. Gas is a measure of how much computing work a transaction requires. A simple transfer uses little gas. A more complex action, such as swapping tokens through a smart contract, uses much more, so it costs more. The total fee is the gas used multiplied by the gas price, and the gas price is what rises and falls with congestion. The gas mechanism on Ethereum is the model many other networks borrowed and adapted.
Fees differ across networks
Not all blockchains charge the same. Ethereum’s main network is known for fees that can climb to $10 or more when busy. Networks built for lower costs, such as Solana, Polygon, and various layer-2 chains, often process the same kind of transaction for a fraction of a cent to a few cents. This is why the network you choose to send a coin on can matter as much as the amount you send.
Before confirming any transaction, check the fee on your wallet’s confirmation screen. It tells you the current cost, and on most apps you can adjust the speed to pay less when you are not in a hurry.