The money side of a commute is four numbers: how far you go, how thirsty your car is, what fuel costs where you live, and what you pay to leave the car somewhere once you arrive. Everything else is multiplication.
The formula
Daily cost = (round trip miles / miles per gallon x price per gallon) + parking and tolls
Worked example
Take a 14 mile drive each way, five days a week, in a car doing 28 miles per gallon, with fuel at $3.50 and $10 a day to park. The round trip is 28 miles, which burns about a gallon, so fuel is $3.50 and the day costs $13.50 in total. Across 48 commuting weeks that is $270 a month and $3,240 a year, on 6,720 miles of driving.
Two inputs deserve a second look. Set the gas price to what you actually paid last time you filled up, because prices vary widely by state and the default in the tool is a neutral placeholder rather than a market rate. And set the commuting weeks honestly: 52 assumes you never take a day off, so most people land nearer 48 once vacation and holidays come out.