diff --git a/src/docs/developers/build/transaction-fees.md b/src/docs/developers/build/transaction-fees.md
index 97e4a2260..7313a36e8 100644
--- a/src/docs/developers/build/transaction-fees.md
+++ b/src/docs/developers/build/transaction-fees.md
@@ -33,6 +33,9 @@ Gas prices fluctuate with time and congestion, but you can always check the curr
 
 ### Base fee
 
+The [base fee](https://eips.ethereum.org/EIPS/eip-1559#simple-summary) is charged for each unit of gas that a transaction uses.
+It is the same base fee for each transaction in the block, and is determined by formula based on the base fee of the previous block and how full that block was.
+
 [The EIP 1559 parameters](./differences.md#eip-1559) have different values in OP Mainnet (and most other OP Stack chain) than those on L1 Ethereum.
 As a result, in every block the base fee can be between 98% and 110% of the previous value. 
 As blocks are produced every two seconds, the base fee can be between 54% and 1,745% of the value a minute earlier.