Oil Change Tracker

Interval averages

Each pair of consecutive oil changes forms one interval. The tracker measures both dimensions of every interval:

• Distance interval: the odometer difference between one change and the next.
• Time interval: the number of days between the two dates.
• Average: the mean across all intervals, so a log with four changes gives three intervals.

Your driving rate comes from the whole log: total distance covered divided by total days elapsed, from the first entry to the last. That rate is what turns a distance limit into a predicted date.

When the next change is due

Two limits run from your last oil change, and the earlier one wins:

• Distance limit: last odometer + your interval. With a known driving rate, the tool projects the date you will reach it.
• Time limit: last service date + your interval in months. Oil ages in the sump even on a car that barely moves, which is why the months limit exists at all.

The status turns amber inside the last 10% of the interval and red once either limit passes. A single entry is enough to get a due date; a second entry unlocks the averages.

Worked example

Last change on 1 March at 42,000 miles, a 5,000 mile / 6 month interval, and an average of 30 miles per day:

distance limit = 42,000 + 5,000 = 47,000 miles, reached in 5,000 ÷ 30 ≈ 167 days, so about 14 August

time limit = 1 March + 6 months = 1 September

The mileage limit arrives first, so 14 August is the due date.

Reminder file

The reminder downloads as a standard .ics calendar file with an all day event on the due date and an alarm one week ahead. Open it to add the event to Apple Calendar, Google Calendar, Outlook, or any other calendar app.