Work out Eth price from getAmountsIn method

Question

I am attempting to create a test arbitrage bot using Uniswap & SushiSwap.

I can successfully get the amount of X tokens I would get for 1 WETH on both dexes. For example:

​

Uniswap: WETH / USDT 1704.93153

Sushi Swap: WETH / USDT 1701.745783

To do this I am using the `getAmountsIn` method and passing in 1 WETH.

async getBuyPrice() {
    const pathToBuy = await this.routerContract.methods
    // getAmountsIn already includes Uniswap & SushiSwap fees in the calculation
    .getAmountsIn(this.swapAmount, [this.swapTo, this.swapFrom])
        .call();
    // TODO: modify the / 1e12 on a per token basis
    return Math.floor(ethers.utils.parseUnits(pathToBuy[0], this.swapToDecimal) * 100) / 100 / 1e12;
}

I then do a simple profit calculation of

if (uniswapPrice > sushiswapPrice) {
return Math.abs(sushiswapPrice - uniswapPrice); 
}

With these basic calculations I get outputs like:

estimated profit on trade WETH/ USDT 3.185746999999992

My issue comes when I want to then take away the TX costs from the profit including gas fees.

I get the gas price back with:

let gasPrice;
   await web3.eth.getGasPrice().then((result) => {
    gasPrice = web3.utils.fromWei(result, 'ether');
});

gas price in Eth 0.000000013596475603

However, this gives me the gas price in Eth whereas `getAmountsIn` allows me to calculate the profit in the token I am attempting to swap, for example 3.1 USDT.

Would I then need to convert `WETH/ USDT 3.185746999999992` into Eth and minus TX fees to work out the true profit? I'm quite new to all of this so am unsure.

Thanks!

Answer 1

const finalProfit = estimatedProfit - gasPrice

Yes you need to do this math.