Gas fees are the transaction costs you pay to use a blockchain network — they compensate validators (or miners) for the computational resources needed to process and validate your transaction. On Ethereum, gas is denominated in gwei (billionths of ETH), and the total fee depends on how complex your transaction is and how congested the network is. A simple ETH transfer might cost $0.50, while a complex DeFi interaction could cost $5-50+ on Ethereum mainnet.
Since EIP-1559 (August 2021), Ethereum uses a base fee + priority tip system. The base fee adjusts automatically based on network demand — when blocks are more than 50% full, the base fee increases; when they're less than 50% full, it decreases. The priority tip incentivizes validators to include your transaction sooner. The base fee is burned (removed from circulation), making ETH potentially deflationary during high-usage periods. Users can set a max fee they're willing to pay to avoid overpaying during sudden spikes.
Use Layer 2 networks (Arbitrum, Optimism, Base) for 10-100x cheaper transactions. Time your transactions for off-peak hours — gas is typically cheapest on weekends and early mornings (US time). Batch transactions when possible. Use gas-efficient protocols that optimize contract calls. Set a reasonable max fee rather than accepting the default. And consider whether you need Ethereum mainnet at all — Solana, Avalanche, and other chains offer sub-penny transaction costs for many of the same DeFi activities.
Before August 2021, Ethereum gas fees were determined by a first-price auction — users bid against each other, and the highest bidders won block space. This created unpredictable fees and significant overpayment. EIP-1559 introduced a base fee that algorithmically adjusts with demand, plus an optional priority tip for faster inclusion. The base fee is burned (permanently destroyed), while the tip goes to validators. This brought predictability — if blocks are full, base fees rise 12.5% per block until demand cools — and introduced ETH's deflationary mechanism. During high activity, more ETH is burned than issued through staking rewards, making the supply shrink.
Several practical tactics can dramatically reduce gas costs. Time non-urgent transactions for low-activity periods (typically Sunday early morning UTC). Use Layer 2 networks (Arbitrum, Base, Optimism) for everyday transactions where fees are typically a few cents. Batch multiple actions into a single transaction when protocols support it. Set custom gas limits — most wallets default to safe overestimates that you can reduce. Use gas tokens like CHI (now mostly deprecated) or specialized aggregators that find optimal gas prices. For approvals, use exact-amount approvals rather than infinite approvals where possible. Watch the gas tracker on Etherscan or Blocknative to time transactions when fees drop.
Different chains take radically different approaches to transaction fees. Solana fees are typically $0.00025 due to its high-throughput design. BNB Chain charges roughly $0.10-0.30 per transaction. Polygon PoS charges fractions of a cent. Avalanche subnet fees are configurable by the subnet operator. Bitcoin fees can range from a few cents to tens of dollars depending on mempool congestion. Layer 2 fees on Ethereum range from 1-50 cents depending on calldata usage. The trade-offs involve decentralization, security, and developer ecosystem maturity — Ethereum users pay more for the most decentralized and battle-tested smart contract environment.
Gas fees spike when block space demand exceeds supply. Major NFT mints, popular token launches, sharp market moves, and viral DeFi opportunities all create spikes. Ethereum mainnet processes only 15-20 transactions per second; when more users want to transact than the network can handle, an auction-like mechanism prices block space to demand. Layer 2 networks largely solve this by handling overflow capacity.
On Ethereum mainnet, you must pay in ETH. Account abstraction wallets (Argent, Safe with paymasters) can sponsor transactions or accept payment in stablecoins, with the wallet provider handling the ETH conversion behind the scenes. On other chains, you typically pay in their native token (SOL, AVAX, MATIC), though some allow stablecoin gas payment.
Gas limit is the maximum amount of computation a transaction is allowed to consume. Gas price is the cost per unit of computation (denominated in gwei, a small unit of ETH). Total fee = gas limit × gas price. A simple ETH transfer uses 21,000 gas; complex DeFi interactions can use 500,000+. The wallet usually estimates these for you, but understanding the components helps you optimize. Setting a gas limit too low causes the transaction to fail while still consuming the gas spent up to that point. Since EIP-1559, Ethereum also separates base fee from priority tip, adding another layer of fee control for power users.