Here's an illustration of my current bike/car fuel savings.
We're having hot weather (40C+ one day) in my neck of the woods at present, so I've commuted by bike all this past week.
The rough difference between covering that 510km in the car (27.54 litres) verses the bike (16.58 litres) is $12.15 at today's fuel price.
That probably won't cover rego, insurance and minor maintenance, so for me there's no net gain financially by riding a bike to work.
The gain is in my mental wellbeing.