How it's worked out: gas fee = gas price (gwei) × gas limit × 10⁻⁹ BNB, then multiplied by the BNB price to get USD. The gas price, gas limit and BNB price are all entered by you; this tool runs entirely in your browser and doesn't fetch prices online. The real on-chain cost is whatever your wallet estimates when you send the transaction.
Want to save on gas?
Read how BNB Chain gas is calculated and how to save on it; the cost isn't only gas — there's also the spread and slippage, broken down in full in fees and slippage. To get the wallet sorted first, see the Web3 Wallet basics.
Paying gas means keeping a little BNB in your wallet. Open a Binance account and wallet first, and stock up a small amount.