Why the driving number is usually understated
Ask someone what their commute costs and they will divide the distance by the MPG and multiply by the pump price. That is the fuel bill, and on a 20 mile each-way commute at 25 MPG it is about $111 a month at $3.30 a gallon. It is also, on most commutes, less than half of what driving actually costs.
The rest sits in three places. Parking at the destination end is a straight monthly charge that people mentally file under something other than commuting. Tolls are small per crossing and large per year, because the crossing count is roughly 42 a month. And the largest line, the one that never appears on a receipt, is what the mileage does to the car: depreciation on a vehicle that will be sold with 60,000 more miles on it, insurance priced partly on annual mileage, tires, brakes, fluids and the scheduled services that arrive on a mileage interval rather than a calendar one.
The default here of 25 cents a mile is a placeholder, not a claim about your car. Work out your own by taking last year's total spend on depreciation, insurance, servicing and repairs and dividing by the miles you actually drove. Cheap old cars driven a lot come out well under it; new cars driven little come out far above it, because depreciation is mostly a function of time rather than distance.
Marginal cost against full cost
The ownership checkbox switches between two different questions, and both are legitimate.
| Question | Setting | What it answers |
|---|---|---|
| Should I drive in tomorrow or take the train? | Ownership off | Marginal cost. The car exists, is insured and is depreciating whether or not you use it today. |
| Should this household run a second car? | Ownership on | Full cost. Dropping the commute could drop the vehicle, so all of its cost is in play. |
| Should I take this job across the metro area? | Ownership on | Full cost, because the mileage is new and the wear it causes is new. |
People argue about which figure is correct. They are answering different questions with the same arithmetic.
Fares are local and this calculator does not guess
Transit fares in the United States are set agency by agency and there is no structure common enough to build in. Some systems charge a flat fare regardless of distance, some charge by distance or zone, some give free transfers within a window and some charge again at every boarding. Many cap daily or weekly spending so that a pass buys itself automatically. Passes may be sold monthly, as a rolling 30 days, or as a stored-value discount. Employers can offer transit benefits from pre-tax income, which changes the effective price by a third or so for anyone who has them, and reduced fares by age, disability or income status are widespread.
So the fare field is an input with no clever defaults behind it. Look up what your trip actually costs, and if a pass is on offer, compare the pass price against your trip count rather than assuming the pass wins. The calculator prints the break-even trip count when you choose the pass option, which is the only number that decides it.
What the comparison leaves out
Some things are genuinely hard to price and are absent by design. Reliability differs: a car that is stuck in traffic and a train that is delayed cost the same minutes but not the same predictability, and a commute you can rely on to within five minutes is worth more than its average duration suggests. Weather, luggage, mid-day errands and picking up children are all reasons a car wins that have no dollar figure. Against that, driving carries a crash risk that grows with exposure, and parking hunts at the destination end are real minutes that never show up in a routing estimate.
The time valuation, if you switch it on, is the crudest part of the page. It multiplies the difference in door-to-door minutes by an hourly rate as though every commuting minute were billable, which none of them are. Its usefulness is not the total it prints but the size of it: seeing that a 20 minute daily difference is 70 hours a year is the point, and what those hours are worth is a judgement you make rather than one a calculator makes for you.
Questions people ask
What should I put for the ownership cost per mile?
Your own figure, from your own records. Add up what the car cost you last year in depreciation, insurance, registration, tires, servicing and repairs, then divide by the miles you drove. Depreciation is the awkward part: take what a comparable car of your age and mileage sells for today against what one a year younger sells for. If you have no records at all, the 25 cent default is a rough middle for a mainstream car driven a normal amount, but it will be badly wrong at both ends. An old paid-off commuter car driven 20,000 miles a year can be under 15 cents; a recent purchase driven 6,000 miles a year can be over a dollar, because the depreciation is spread across so few miles.
Should I count the time I spend commuting as a cost?
Only if you are going to be honest about the rate. The time is real, the difference between modes is real, and 20 minutes each way is about 70 hours a year. What is not obviously true is that those hours are worth your wage. You are not being paid for them either way, so the question is what you would otherwise do with them, and the answer is rarely paid work. Time on a bus or train can be spent reading, working or doing nothing in particular; time driving cannot be spent on anything else at all. Many people who use this field find that half their hourly rate produces a result they actually agree with.
How do I handle a hybrid schedule where I go in two or three days a week?
Set the commuting days figure to the days you actually go in — nine days a month for two days a week, thirteen for three. The parking line needs attention though. A monthly parking contract does not get cheaper because you use it less, so leave it at the full monthly rate if that is what you pay; if you pay daily, multiply the daily rate by the days and put that in. The same applies to a transit pass: at low trip counts the per-trip option often beats the pass, and the break-even trip count the calculator prints will tell you which side of the line you are on.
Does this work for an electric car?
Not directly, because the fuel fields are in gallons and dollars per gallon. You can force it by converting: divide your cost per mile for electricity by 1 and enter it as a fuel price with MPG set to 1, which is ugly but arithmetically correct. It is cleaner to work the driving side out on a page built for it and bring the monthly total back here. Bear in mind that per-mile ownership costs for an EV are not the same as for a gasoline car either — less scheduled maintenance, different depreciation, and a battery whose replacement cost sits a long way out but is not zero.