"Full" depends on what you vacuum
A vacuum bag doesn't wear out on a calendar. It stops working when its pores clog or it physically fills, and what you vacuum decides which happens first. Miele's own support notes spell out both extremes:
- Fine dust such as sawdust, plaster, sand, or flour clogs the bag's pores quickly. Suction drops, and the bag indicator may read full even though the bag looks mostly empty.
- Hair, lint, and carpet fluff take up space without clogging much, so a bag can be stuffed full before the indicator reacts.
What shortens the interval
Pets are the biggest factor. Shedding fills bags with bulky hair, and pet dander is exactly the kind of fine dust that clogs pores. Vacuuming often, a larger home, and dusty conditions (renovation, dirt roads, a workshop) all shorten the interval further.
The calculator starts from about two months for a medium home vacuumed weekly and adjusts from there.
When to change the bag
Change the bag when the indicator shows full, or sooner if suction drops noticeably. Running on a clogged bag makes the vacuum work harder and cleans worse, and a bag bursting from overfilling is a far bigger mess than changing it a little early.