What it means
Before sending, a node simulates the transaction to work out how much gas it needs. If that figure exceeds the gas limit supplied, or exceeds what the account can afford at the current price, the transaction is refused at this stage. Nothing is broadcast and nothing is charged.
The word "allowance" here refers to the gas allowance for the transaction. It is unrelated to a token approval allowance, which is a different concept with an unfortunately similar name.
Why it happens
The gas limit is set below what the operation needs
A custom or reused limit that does not cover the work required.
The account cannot afford the estimated cost
If the estimated gas multiplied by the price exceeds the native balance, the transaction cannot proceed. This overlaps with insufficient funds for gas.
The transaction would revert anyway
A transaction that cannot succeed sometimes produces an inflated or failed estimate. The underlying problem is the revert, not the gas.
How to fix it
- Remove any custom gas limit and let the wallet estimate.
- Check the native balance on the network in question and top it up if it is short.
- If estimation keeps failing, test whether the transaction can succeed at all — the cause may be a revert condition rather than gas. See execution reverted.
How to avoid it
Keep a native balance comfortably above the typical cost of the transactions you make, and avoid carrying custom gas limits between different operations.
Frequently asked
Is this about a token approval?
No. Despite the word allowance, this refers to the gas made available for the transaction, not an ERC-20 spending allowance.
Was I charged?
No. The transaction was rejected during estimation and never broadcast, so no computation was performed and no fee was taken. This is unlike an out-of-gas or reverted transaction, where execution happened and the fee is consumed.
Why does the estimate seem so high?
Sometimes because the transaction would fail if executed. An estimate for a doomed transaction is not meaningful; investigate the failure condition instead.
Sources & further reading
- Ethereum: gas and fees
Gas units, limits and the fee calculation.
- Ethereum: transactions
Transaction fields including nonce, gas limit and fee caps.
- MetaMask: user guide to error codes
Wallet-level explanations of the error strings surfaced to users.
- Etherscan: reasons for failed transactions
How a reverted transaction is displayed and what state is rolled back.
Sources checked on 18 September 2026. Network features and platform support can change; check the relevant provider before acting.
AI-assisted editorial content; no independent expert review is claimed. Error behaviour varies between wallets, networks and client versions. This is educational information, not investment advice. Read our editorial policy.