Gas estimation for a method

[fricpto]

Hello,I have a hardhat project that have a file that does this const arbitrage = new ethers.Contract(config.PROJECT_SETTINGS.ARBITRAGE_ADDRESS, IArbitrage.abi, provider); and it is imported in another js file and that file has a function that wants to estimate gas for a specific function inside the contract.sol file:

const account = new ethers.Wallet(process.env.PRIVATE_KEY, provider)
        const arbitrageWithSigner = arbitrage.connect(account);
const estimatedGasLimit = await arbitrageWithSigner.executeTrade.estimateGas(
            [await _exchangePath[0].router.getAddress(), await _exchangePath[1].router.getAddress()],
            [_token0.address, _token1.address],
            _poolFee,
            borrowAmount
            // ethers.parseUnits("1", _token0.decimals) Use a nominal amount for estimation
        );

I have logged the method estimateGas() and the executeTrade() they both exist

typeof arbitrageWithSigner.executeTrade: function
typeof arbitrageWithSigner.executeTrade.estimateGas: function

I also checked for executeTrade() method in my abi and it exist but I'm getting this error:⚠️ Profitability check failed: Cannot read properties of undefined (reading 'executeTrade')"},I'm using Ethers version: 6.15.0,I logged it to make sure that I'm correct.I'm using executeTrade() in an another function in the same file and I'm not getting any error from it.
Now what is the correct way to estimateGas()?

[wesleysmyth]

In ethers v6, gas estimation for contract methods uses the .estimateGas namespace on the contract:

Basic gas estimation

import { Contract, JsonRpcProvider } from 'ethers';

const provider = new JsonRpcProvider('http://localhost:8545');
const contract = new Contract(contractAddress, abi, provider);

// Estimate gas for a specific function call
const gasEstimate = await contract.transfer.estimateGas(
  '0xRecipient',
  ethers.parseUnits('100', 18)
);

console.log('Gas estimate:', gasEstimate.toString());

With a signer (for state-changing calls)

const signer = await provider.getSigner();
const contract = new Contract(contractAddress, abi, signer);

const gas = await contract.swap.estimateGas(
  tokenIn,
  tokenOut,
  amountIn,
  minAmountOut,
  { value: ethers.parseEther('0.1') } // if payable
);

Dry-run first with staticCall

Before estimating gas, validate the call will succeed:

try {
  // staticCall simulates without state changes — catches reverts
  const result = await contract.swap.staticCall(tokenIn, tokenOut, amount);
  console.log('Would return:', result);

  // If staticCall passes, estimate gas
  const gas = await contract.swap.estimateGas(tokenIn, tokenOut, amount);
  console.log('Gas needed:', gas);
} catch (err) {
  console.error('Call would revert:', err.reason);
}

Common gotchas

1. Signer needs funds for estimation

If the function transfers ETH or tokens from the signer, the node simulates the full execution. If the signer address has insufficient balance, the estimation will fail with UNPREDICTABLE_GAS_LIMIT.

Workaround for read-only estimation:

// Use a provider (not signer) and set `from` in overrides
const gas = await contract.swap.estimateGas(
  tokenIn, tokenOut, amount,
  { from: '0xAddressWithFunds' }
);

2. Hardhat fork mode

On Hardhat forks, gas estimation can fail if the forked state is stale. Use hardhat_reset to refresh, or increase the block gas limit:

// hardhat.config.ts
networks: {
  hardhat: {
    gas: 30_000_000,
    blockGasLimit: 30_000_000,
  }
}

3. Adding buffer

Gas estimates are lower bounds. Add a buffer for safety:

const estimate = await contract.method.estimateGas(args);
const gasLimit = estimate * 120n / 100n; // 20% buffer

const tx = await contract.method(args, { gasLimit });