How to know what maintenance your car is due for

A job is due when you reach its mileage or its months, whichever comes first. Take today's odometer reading, subtract the reading when the job was last done, count the months since that date, and compare both to the intervals in your owner's manual. The one that's closer to its limit decides.

This is for a car you drive in miles, with a manual or a maker's schedule to hand. It can't tell you what your car's intervals are, and it can't judge a job that has no date behind it. For that, start with a recorded date, even a rough one you label as rough.

An example: four jobs on one car

Say it's August 20, the odometer reads 52,300, and these are the intervals and last-done facts. They're an illustration, not your car's schedule.

Reading the example

Look at the oil line. Only 4,200 of 5,000 miles are used, so it feels early. But 5.6 of 6 months are gone, so the months limit is the one that's about to be reached. A car that sits in a driveway most of the week hits the months first. A car that does a long commute hits the miles first.

The brake fluid row is the one to notice. No date means no answer, and a guessed date would give a false one. Leave it blank and say so, then find out the real date or start the clock from the next time it's done.

The method, five steps

1. Find the intervals. Your owner's manual lists each job by miles, by months, or both. Many manuals also have a second, shorter schedule for severe driving, such as towing, mostly short trips, heavy dust or extreme heat or cold. If that's how you drive, use the shorter one. This guide shows where to look in the manual.
2. Write down when each job was last done and the odometer reading at the time. A receipt, a sticker on the windshield or a shop's records can supply it. If you did it yourself, your own note does.
3. Read the odometer today. Write the number down beside the date, because the answer is only as good as this reading.
4. Subtract. Today's miles minus the last-done miles is the distance since. Count the months from the last-done date to today.
5. Compare each to its interval. Whichever is further along its limit is the one that decides, and it tells you how much is left. If both are past, it's due now.
6. If the manual gives only miles or only months for a job, use the one it gives. Don't invent the other.

When the answer is wrong

• The odometer reading is stale. If you last looked three weeks ago and you drive a lot, every miles figure is low. Look again before you decide anything.
• There's no last-done date. Don't fill it in from memory of "about last spring". Mark the job as unknown, and either check with the shop that did it or treat the next service as day one. If you bought the car without records, this covers where to look.
• You drive in hard conditions and used the normal schedule. The severe-duty schedule usually comes round sooner, so the job you think is fine may be due.
• The manual and the shop disagree. Shops sometimes suggest sooner intervals than the maker does. You can ask them to show you why for your car, and it's your call. What's due by the maker's schedule and what a shop recommends are two different questions, so keep them apart in your notes.
• You have more than one car. The sum is the same, but the notes get mixed. Keeping each car's jobs on its own line avoids doing the arithmetic on the wrong odometer.

Questions people ask

Where the Companion fits

Vehicle Maintenance Companion does the subtraction from the numbers you enter. You type each job's interval in miles, months or both, and when it was last done, and its Due view lists what's due across every car you own, most urgent first. It says so plainly when nothing is due. A job with no recorded date shows as nothing to judge yet, never as overdue. It works in miles only, and it uses your intervals, not a factory schedule. It also asks you to update the mileage once it's more than 30 days old, because the answer depends on it.