How this calculator works
The calendar span of the period, including both end dates, is scaled by how many days a week you normally commute, so a five day week over 85 days gives about 60 commutes. Each commute is assumed to be a return trip, so travel time and distance are doubled. For a car, total kilometres are divided by fuel economy to get litres burned, which are priced and multiplied by the carbon dioxide released per litre. Public transit costs the return fare, and walking or cycling costs nothing to run. Carbon dioxide is reported only for cars, because transit and active travel emissions depend on vehicle occupancy and are negligible per commuter in comparison.
Formula
Commutes avoided = calendar days in the period x commute days per week / 7, rounded down. Time saved = commutes x 2 x one way time. Car fuel = commutes x 2 x one way distance / fuel economy. Car cost = fuel x price per litre. Car CO2 = fuel x 2.31 for petrol or 2.68 for diesel. Transit cost = commutes x 2 x one way fare. Active travel cost = 0.
Worked example
From 5 January to 30 March inclusive is 85 days. At five commute days a week, that is 60 commutes avoided. A 30 minute each way journey saves 60 hours. Driving 12 km each way at 8 L/100 km covers 1,440 km and uses 115.2 litres, costing 190.08 at 1.65 a litre and releasing 266.11 kg of carbon dioxide for a petrol car.
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Frequently asked questions
Why is the commute count rounded down?
The period contains whole days, but you cannot make a fraction of a commute. Rounding down avoids claiming a trip you would not have taken, so the time and money saved are conservative.
Why is carbon dioxide shown only for cars?
A car burns fuel in direct proportion to the distance driven, so the figure is well defined. Transit emissions depend on how full the vehicle is and how the electricity or fuel was produced, and walking and cycling produce none directly. Reporting zero for those modes keeps the comparison honest rather than inventing a number.
Does the money saved include wear on the car?
No. It includes only fuel, or the transit fare. Tyres, servicing, insurance and depreciation also fall when you drive less, so the true saving is higher, but those costs vary too much to assume.
What if I worked from home only part of the period?
Set the start and end dates to the days you actually stayed home, or lower the commute days per week if you still travelled occasionally. The calculation scales linearly with both.