Calculate weekly commute fuel cost.
A commute is a round trip, so the daily distance is twice the one-way figure — the single most common error in commute budgeting. Fuel cost per mile is the pump price divided by economy, and multiplying through by days gives the weekly figure. The annual line uses 46 working weeks rather than 52 to allow for leave and public holidays, which keeps the yearly number honest rather than inflating it by about an eighth.
Daily cost
Daily = one-way miles x 2 x (fuel price / mpg)
Rollups
Weekly = daily x commuting days; annual = weekly x 46 working weeks
No, it is only the fuel. Depreciation, tyres, servicing and insurance mileage bands typically add as much again, which is why per-mile ownership figures land far above fuel alone.
A cold engine runs rich and the catalyst is inactive for the first few miles, so trips under about five miles can consume 20 to 40 percent more fuel per mile than the steady-state figure.