For a first USDT swap, estimate the Energy cost at the current rate of 100 sun per Energy, or 0.0001 TRX, then leave additional TRX for Bandwidth. There is no single reserve that fits every trade: the contracts called and the resources already available to your wallet change the amount.
A token swap uses Energy as well as Bandwidth
A TRON swap that trades TRC-20 tokens such as USDT or JST runs smart-contract code, which consumes Energy. Bandwidth pays for the size of the on-chain transaction. If your wallet lacks enough of either resource, the network can burn TRX from its balance to cover the shortfall.
Think of the trade as a small chain of actions. A token may first need an approval transaction that lets a swap contract use it; the swap then calls one or more contracts to exchange the tokens. Approval may be a separate transaction, so budget for it if your wallet or service says one is needed. A direct-wallet service such as TRON swap is one way to exchange TRX or TRC-20 tokens, but the resource cost still depends on the contracts and your wallet’s available resources.
Estimate Energy before choosing your reserve
Start with the Energy estimate shown for the transaction, if available. Multiply the Energy your wallet may have to pay for by 0.0001 TRX; for example, 150,000 Energy with no staked, delegated, or contract-supplied Energy would cost 15 TRX at the current burn rate. That is an illustration, not a quote for a particular trade.
Why can the actual amount differ? The receiving pool, token contract, and current network load affect the computation. TRON’s dynamic Energy model can raise the Energy cost of heavily used contracts, and a contract may cover some of the caller’s Energy. Your wallet’s remaining Energy also matters: only the uncovered amount needs another source, such as TRX burn.
Bandwidth has a separate price. Each transaction byte uses one Bandwidth; accounts currently get 600 free Bandwidth per rolling 24 hours. If you have none left, the current burn rate is 1,000 sun (0.001 TRX) per byte, so a 300-byte transaction would use 0.3 TRX. Actual transaction size varies.
Keep a reserve that covers the whole attempt
Use the estimate for the swap and add any separate approval cost, then leave a modest margin for changing resource use. Check the wallet’s available Energy and Bandwidth first; staked or delegated resources can reduce how much TRX the network burns. If you cannot get an estimate, do not assume a standalone token transfer’s cost predicts a swap’s cost. A TRON swap can run more contract code than a simple transfer.
Before signing, confirm the wallet is on TRON, the token and amount are the ones you intend to trade, and enough TRX remains after the proposed transaction to cover its resource charge. The transaction’s fee limit caps the TRX available for Energy burn; setting it too low can make the contract call fail even when your wallet holds more TRX. For a first trade, an estimate that includes any required approval is the practical basis for deciding how much TRX to leave in the wallet.