Bicycle Commuter Act of 2021 This bill modifies provisions relating to the tax exclusion for employer-provided fringe benefits for bicycle commuting. Specifically, the bill (1) repeals the suspension (for the period between 2018 and the end of 2025) of the exclusion, (2) includes bikeshare (a bicycle rental operation providing for pick up and drop off) and low-speed electric bicycle within the definition of bicycle for purposes of the exclusion, and (3) modifies the limitation on the exclusion to provide for a specified monthly limitation amount (i.e., 30% of the parking fringe benefit amount).