Wrong estimation of gas while contract deployment

Question

I have a smart contract:

pragma solidity 0.5.3;

import "./ERC20.sol";

contract Transfer {

  ERC20 private erc20iface;
  address private _owner;

  modifier validOwner() {
    require(msg.sender == _owner);
    _;
  }

  constructor() public {
    _owner = msg.sender;
  }

  function () external payable {}

  function transferTo(address[] memory receivers, uint[] memory amounts, address token) {
    //Some code uses ERC20 methods/or simple transfers with .call()
    }
 }

When I try to deploy the contract in Remix it shows the transaction cost = 424652 gas. However when I try to estimate gas limit with web3 .estimateGas()

const contractData = {
      data: '0x123',
      arguments: []
    };

    const contract = new web3.eth.Contract(CONTRACT_ABI).deploy(
      contractData
    );
    const gasLimit = await contract.estimateGas();

I get gasLimit = 409652 And when I try to deploy, I receive an error: Out of gas

But if I use the amount of gas from Remix (424652) it works fine.

What can be the reason of such differences (15000 gas, like if .estimateGas is missing ERC20 import)? And how to estimate the gasLimit with .estimateGas() correctly?

Answer 1

Since you aren't including the creator address in the estimateGas() version, it defaults to the 0x0 address. So in the constructor, it sets _owner = 0x0, which only costs 5k. The Remix version uses a non-zero creator though, which causes a 20k cost. That accounts for the 15k savings in estimateGas()