Keep AVAX in your wallet to pay for every Avalanche C-Chain transaction. Before swapping, check the wallet’s gas estimate and leave room for any separate token approval. For example, if approval and swap together are estimated at 0.00046 AVAX, a larger reserve gives you room for another transaction or a changing estimate.
How much AVAX should you keep aside?
Set aside enough AVAX for the swap’s estimated fee, any approval fee, and a buffer. Gas is the network’s measure of the work a transaction uses; the fee depends on that work and the current gas price. A swap involving a complex token or pool can use more gas than a simple transfer.
Here is an illustrative calculation, not a quote for a particular swap. At 2 nAVAX per gas unit, a 50,000-gas approval would cost 0.0001 AVAX, while a 180,000-gas swap would cost 0.00036 AVAX. Together that is 0.00046 AVAX; you could keep about 0.005 AVAX available as a cushion, then check the wallet’s estimate before signing.
Blackhole swap is one example of a service for swapping tokens or providing liquidity on Avalanche C-Chain. The site is blackholeswap.app.
Why might one swap need two transactions?
A token swap can need a separate approval before the swap itself. Approval gives a smart contract, which is code running on the network, permission to use a set amount of your token. If your wallet has not already granted that permission, approving and swapping each uses AVAX for gas.
Check the wallet’s transaction details before signing each step. If an attempted transaction fails after it starts running, it can still use gas, so keep enough AVAX for a retry. When comparing ways to swap, count the approval as part of the cost; the swap’s displayed estimate alone may not cover it. For Blackhole swap, the same rule applies: budget for the transactions your wallet asks you to approve.
Can I pay Avalanche C-Chain gas with the token I’m swapping?
No. Transactions on Avalanche C-Chain use AVAX for gas, even when the swap uses another token. Keep some AVAX in the wallet that will sign the transaction. Holding the token you plan to swap does not by itself cover the network fee.
What if I have enough AVAX for the swap but not the approval?
The approval is a separate transaction, so it needs its own gas. If the wallet shows an approval step, make sure your AVAX balance can cover that estimate as well as the later swap. You may need to add AVAX before proceeding; otherwise, the swap cannot complete.
Should I use the exact gas estimate as my reserve?
Use the estimate to plan, but leave extra AVAX in case you need an approval, a retry, or another transaction. The exact amount depends on the gas each transaction uses and the network’s fee when it is included. Check the wallet’s current estimate again before signing.