Three numbers, and only one of them is comparable
Cost per change is what you feel at the counter. Cost per year is what shows up in a household budget. Cost per mile is the only one of the three that lets you compare two options honestly, because it is the only one that accounts for both the price and the interval at once.
The arithmetic is short. Cost per change is the oil plus the filter plus anything else consumed, plus labour if someone else is doing it. Changes per year is annual mileage divided by the interval. Cost per year is those two multiplied. Cost per mile is cost per change divided by the interval, and it is the figure that settles arguments:
Cost per mile = (oil + filter + labour) ÷ interval in miles
A $41 change at 5,000 miles is 0.82 cents a mile. A $62 change at 10,000 miles is 0.62 cents. The second one costs half again as much on the day and is a quarter cheaper over the distance. That reversal is the entire reason this page shows both columns rather than one.
Jugs, quarts and the leftover
Oil is priced one way and consumed another. A five-quart jug is usually the cheapest unit, but engines take 4.5 or 5.7 or 6.2 quarts, so you buy in fives and use in awkward fractions. This calculator rounds up to whole jugs and charges you for all of them, which is the honest accounting for a single change — the leftover only becomes free oil if you use it, topping up between changes or on a second vehicle running the same grade.
If you run more than one vehicle on the same specification, buying the larger container and pricing by the quart is generally the cheaper route, and the per-quart mode here lets you price it that way. Note also that a "5 quart" jug and a "5 litre" jug are not the same thing: five litres is 5.28 quarts, which is occasionally the difference between one container and two.
What is actually being compared when people argue about oil
| Variable | Effect on cost per change | Effect on cost per mile |
|---|---|---|
| Oil grade or brand | Direct — the biggest single line item | Only matters alongside the interval it permits |
| Interval length | None | Inversely proportional — doubling it halves the figure |
| Filter choice | A few dollars | Small, unless the interval depends on it |
| Shop versus doing it yourself | Usually the largest single difference | Same, scaled by interval |
| Number of vehicles | None | None — it scales the annual total only |
The pattern is that the interval is a multiplier on everything else, which is why arguing about the price of a jug while ignoring the interval is arguing about the small term. It is also why the comparison has to be between combinations that are each actually valid for the engine, rather than between the cheapest oil and the longest interval.
Other fluids run on the same arithmetic
Nothing in this calculation is specific to engine oil. Transmission fluid, coolant, differential and transfer-case oil, brake fluid and power steering fluid all reduce to a capacity, a price per unit, sometimes a filter, and an interval — and the same cost-per-mile figure comes out. The intervals are longer, often by an order of magnitude, so the per-mile numbers are small enough that people never bother to work them out, which is a shame, because it is the accumulation of small per-mile figures that makes up the real cost of running a vehicle. Enter a differential's two quarts against a 60,000 mile interval and you will see how little it contributes next to the tires.
On intervals
This page will not tell you how often to change your oil, and any page that tells you without asking what you drive and how is guessing. The interval belongs to the engine manufacturer, it is published in the maintenance schedule for your specific engine, and it differs between the normal and severe schedules for reasons that have nothing to do with money — short trips that never reach operating temperature, sustained towing, dusty conditions and extreme heat or cold all age oil faster than steady highway miles do. Many modern vehicles supersede fixed mileage entirely with an oil-life monitor that models how the engine has actually been used. Put the manufacturer's figure into this calculator and let it tell you what that costs. Do not put a figure in because it makes the cost per mile look better.
Questions people ask
How do I work out the cost per mile of an oil change?
Add up everything consumed by one change — the oil, the filter, the drain plug washer, and the labour if you are paying someone — then divide by the interval in miles. A $41 change every 5,000 miles is 0.82 cents per mile; a $62 change every 10,000 miles is 0.62 cents. Cost per mile is the only figure that lets you compare two options fairly, because it folds the price and the interval together, and the ranking it produces frequently reverses the ranking by shelf price. To turn it into an annual figure, multiply by the miles you actually drive rather than the miles you think you drive — the odometer over a year is a better source than an estimate, and if the odometer itself is off because of a tire size change, that error propagates into this number too.
Is synthetic oil worth the extra cost?
On cost alone the question resolves to arithmetic you can do here: put the conventional price and its interval in one column, the synthetic price and its interval in the other, and compare cost per mile. Synthetic typically costs more per quart and is specified for longer intervals, and whether the longer interval outweighs the higher price depends entirely on the two intervals involved. But the cost comparison is only valid if both options are actually approved for your engine. Many engines now specify a synthetic oil outright, or a viscosity grade that is only manufactured as a synthetic, in which case there is no comparison to make. The non-cost arguments — cold-start flow, resistance to breaking down at high temperature, behaviour in turbocharged engines — are real and are not modelled here. Start with what the manual specifies, then use this page to price the options that specification allows.
How many quarts does my car take?
It is in the owner's manual, in the capacities table, and it is worth reading the exact line because the figure usually differs depending on whether the filter is being replaced too. Typical passenger-car capacities run from about 4 to 6 quarts, larger engines 6 to 8, and some V8s and diesels considerably more. Do not estimate from the dipstick or from a similar car: capacity varies between engines within the same model, and getting it wrong in either direction matters. Fill to the manual figure, run the engine briefly, let it settle, then check the dipstick and adjust — the stated capacity is nominal and a little oil always stays behind in the galleries and cooler.
Can I use this for transmission fluid or coolant?
Yes, and the arithmetic is identical. Enter the capacity in quarts, the price per quart or per container, any filter or gasket that goes with the service, and the interval. The output means the same thing: cost per service, per year and per mile. The main adjustment is that the intervals are far longer, so set the projection window to something that spans at least one service, otherwise the annual figure is a fraction of a service and reads oddly. Two cautions specific to other fluids. Specification matters more, not less — the wrong transmission fluid or the wrong coolant chemistry causes expensive damage that the wrong oil brand generally will not. And several of these services are not simple drain-and-fills; a transmission may need a flush or a specific fill procedure to reach its stated capacity, which changes both the labour figure and how much fluid you actually buy.