Keep some TRX in the wallet that will make the swap; the amount depends on the contract call and your available network resources. A TRC-20 token is a token issued on TRON, such as USDT. You need TRX for any fee the network cannot cover with Energy or Bandwidth.
What does the network charge?
A wallet-based TRON swap sends a smart-contract call: a request to run code on TRON. The call may involve token contracts and a swap contract, so its Energy use can vary by token and route. Energy pays for that code; Bandwidth pays for the transaction’s size.
Bandwidth has a small free daily allowance for an active account, but Energy has no free allowance. Staked or delegated Energy can cover some of the call, and a contract’s operator may cover some too. If those sources fall short, TRON burns TRX from the sending wallet.
How can you estimate your TRX reserve?
Use the wallet’s transaction estimate as your starting point, then check how much Energy your account already has. For example, if your share is 110,000 Energy and no resources cover it, the current network rate of 100 sun per Energy works out to 11 TRX. A sun is one millionth of a TRX.
That is an example, not a fixed swap price. At that rate, every 10,000 uncovered Energy adds 1 TRX. The actual amount depends on the transaction’s Energy use, the resources available, any share covered by the contract operator, and current network parameters.
Before approving a TRON swap, check that the wallet has both the token you want to exchange and enough TRX to cover its estimated shortfall. If you are swapping into TRX, keep a reserve anyway: the network needs the sending account’s TRX for fees, even if TRX is the expected output.
What if the estimate changes or the swap fails?
A smart-contract transaction has a fee limit, which caps the Energy budget the sender allows for that call. It is a ceiling, not a quoted fee: the network charges for resources used, up to that limit. A busy contract can also use more Energy under TRON’s dynamic Energy rules, so leave room above a close estimate.
If the call runs out of its allowed Energy, it can fail and still consume resources already used. For a first attempt, avoid sending your entire TRX balance into the swap. Leave enough for the estimated fee and a modest buffer; check the estimate again if you change the token or route.
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