Yes, foundation expires - and it is the date you open it, not the date you buy it, that usually matters. The little open-jar symbol with a number like “12M” is the period-after-opening (PAO): how many months the product stays safe and effective once you first break the seal.
What the PAO number means
“12M” means twelve months after opening; “6M” means six. Liquid foundation typically carries a 6-12M rating and serums 3-6M (sources: vivianewoodard.com, no7beauty, ~2026). After that window, texture, color, and active ingredients can degrade even if the bottle is not empty.
When expiry costs you money
If a bottle would take longer to use up than its PAO allows, you are paying for product you will throw away. That is most common with large sizes used a few times a week, or backup shades you rotate slowly. The smaller bottle is often cheaper in practice once you count the waste.
Check yours before you buy bigger
The longevity calculator above compares how long your bottle lasts on usage against its PAO date and flags whichever runs out first - including an estimate of the dollars you would waste if it expires before you finish it.