My 2021 is going in or its annual service next week.
It was last serviced (oil etc) a year ago at 15K miles.
It now has 20K miles.
For the last month I have been getting "Service Due" alerts.
Are these time related or mileage related schedules.
Certainly does not fit with the 16K oil change (that nobody on this forum follows!!)

 

On the newer cars it's time or mileage, so it will give you the warning when you approach a year regardless of mileage, or when you approach the 16K regardless of time. On my '23, it approached 1 year when I had 5K on it and I got the warning.

 

it's just a reminder. I do my own routine maintenance on my XF. Whenever Sevice Indicator light appears in the instrument panel I just do a reset. It's easy to do,

 

It also can happen when the dealer (often) forgets to reset the service date, so it comes on prematurely.

To reset the maintenance indicator:

1) Set ignition on
2) Open hood
3) Open driver's door
4) Fully depress both accelerator and brake pedals for 10 seconds
5) Turn off ignition

If the message still appears, try again.

 

Even on our early 2014, the service reminder is a time-based item. It starts at about 6 weeks from the last reset, then gets more insistent as the anniversary of the last reset gets close.

We change our oil/filter and do other services yearly, only 2000-3000 miles apart.