EIP-1559 Explained: Base Fee, Priority Fee and Max Fee

By the GasNow team · Updated October 9, 2026

What EIP-1559 changed

Before August 2021, Ethereum used a simple first-price auction: you named a gas price, miners picked the highest bidders, and users routinely overpaid because they had to guess what everyone else would bid. EIP-1559, activated in the London upgrade, replaced that auction with a protocol-computed base fee plus an optional priority fee. The goal was predictable pricing, fewer overpayments and a fee that cannot be gamed by block producers.

The three numbers in every Ethereum transaction

• Base fee per gas. Set by the protocol for each block. Every transaction in the block pays the same base fee, and that ETH is burned, removed from supply permanently.
• Max priority fee per gas (the tip). What you offer the validator on top of the base fee. In calm conditions a tiny tip is enough; during congestion, higher tips get ordered first.
• Max fee per gas. The absolute ceiling you are willing to pay per unit of gas. It protects you if the base fee rises between signing and inclusion.

You actually pay base fee + tip, never more than the max fee. If the max fee is higher than base fee plus tip, the difference is simply not charged. That is why wallets can safely set a generous max fee: it is a cap, not a bid.

How the base fee moves from block to block

Each block has a gas target equal to half of the block gas limit. If a block uses more gas than the target, the next block's base fee rises; if it uses less, the base fee falls. The maximum change is 12.5% per block. Because blocks arrive every 12 seconds, a sustained surge in demand can multiply the base fee several times within a few minutes, and it decays just as quickly once demand fades. This is the pattern you see in GasNow's Ethereum gas history: short, sharp spikes followed by a return to the baseline.

Worked example

Suppose the base fee is 0.8 gwei and you set a tip of 0.1 gwei and a max fee of 2 gwei. You send a token transfer that uses 65,000 gas.

• Price per gas actually charged: 0.8 + 0.1 = 0.9 gwei.
• Total fee: 65,000 × 0.9 = 58,500 gwei = 0.0000585 ETH.
• Burned: 65,000 × 0.8 = 52,000 gwei. Paid to the validator: 6,500 gwei.
• The 1.1 gwei difference between your max fee and what was charged is never taken.

Why your transaction might wait

If the base fee rises above your max fee, your transaction cannot be included until the base fee comes back down. It stays pending in the mempool. You can wait, or replace it with a higher max fee using the same nonce. The stuck transaction guide walks through both options.

How GasNow's Slow, Standard and Fast tiers relate

GasNow reads Etherscan's gas oracle and, as a fallback, the eth_feeHistory RPC method, which reports recent base fees and the tips paid at different percentiles. Slow, Standard and Fast correspond to progressively higher tips over the current base fee. When the network is quiet the three tiers are almost identical, because a minimal tip already gets you into the next block.

Key takeaways

• The base fee is set by the protocol and burned; you cannot negotiate it.
• The tip is the only lever you control for priority.
• The max fee is a safety cap, and unused headroom is not charged.
• Base fee changes at most 12.5% per block, so spikes build and fade within minutes.