Why are transactions sometimes "pending"?
Understanding network load, mempool congestion, and deterministic fees.
Network Processing & The Mempool
When you sign and submit a transaction, it doesn't instantly appear on the blockchain. It first goes into the Mempool — a waiting area for unconfirmed transactions.
High Network Load
Cardano processes blocks roughly every 20 seconds. Each block has a maximum size limit. During times of massive activity (like major NFT drops, popular DEX launches, or extreme market volatility), there are more transactions being submitted than can fit into the next block.
When this happens, your transaction might sit "pending" in the mempool for several minutes (or rarely, hours) until a block producer selects it.
The Advantage: No Failed Gas Fees
On Ethereum, during high congestion, users enter "gas wars", blindly bidding higher fees to get processed quickly. If they fail, they still lose the fee money. On Cardano, fees are strictly deterministic based on the transaction's data size, not an arbitrary bidding war.
If your transaction is pending during high load, you just have to wait. It will either eventually process for exactly the low fee you agreed to, or (if you cancel/timeout via your wallet) it simply vanishes from the mempool and you lose absolutely zero ADA in fees.