Before bridging, keep gas on the network where your next transaction will happen: ETH for Ethereum and MNT for Mantle. Gas is the small network charge for processing a transaction, and it is separate from the token you are moving. The Mantle Bridge for MNT is one way to move assets between the two networks, but the asset you bridge does not always cover your next gas charge.
Ethereum transactions use ETH for gas, while Mantle transactions use MNT. This stays true even if you are moving USDT: you pay gas in the network’s currency, not in USDT.
A Layer 2 is a network that processes transactions alongside Ethereum and connects back to it. Mantle is a Layer 2, so a transfer can involve costs on both networks. The amount changes with network activity and the transaction itself, so check the wallet’s fee estimate before signing.
For example, imagine you want to bridge 100 USDT from Ethereum to Mantle. You need ETH in your Ethereum wallet for the transfer, and possibly a separate token approval. Once the USDT arrives, you will need MNT to send or swap it on Mantle.
For an Ethereum-to-Mantle deposit, budget ETH for the deposit and, when required, a USDT approval. An approval lets the bridge contract handle a set amount of your token; it is its own Ethereum transaction and does not move the USDT by itself.
After the deposit reaches Mantle, later actions use MNT. If you plan to swap USDT, send it to another wallet, or withdraw it, leave enough MNT to pay for that action. Bridging your entire balance of a token does not provide gas for those later steps.
The return trip also needs gas on both sides. A withdrawal starts with a Mantle transaction, paid in MNT. Claiming the funds on Ethereum requires an Ethereum transaction, paid in ETH, after the withdrawal is ready. Keep some ETH in the wallet that will receive and claim the withdrawal.
For a simple round trip with USDT, the practical plan is ETH for the Ethereum approval and deposit, MNT for the Mantle withdrawal, and ETH for the later claim. The Mantle Bridge transfer is one part of that sequence; each network charges for its own transactions.
There is no fixed gas amount that fits every transfer. Ethereum fees can rise with network demand, and more complex transactions may use more gas. Read the wallet’s estimate for each transaction when you are ready to sign, and keep a little extra of that network’s gas currency for a retry or follow-up transaction.
Do not treat MNT held on Ethereum as gas on Mantle. It is on a different network until moved there, just as ETH on Mantle is not ETH available to pay Ethereum gas. Check the wallet’s selected network and the currency shown beside each fee estimate.
Before signing, check: