A supplement label reports each nutrient as a percentage of a daily value. That reference figure comes from a defined process, and the process explains why the number should not be read as a personal target.
Requirements are estimated from measured endpoints
Committees establishing intake references begin by choosing a measurable endpoint that indicates adequacy, such as the level at which a deficiency sign disappears or a body store is maintained.
Studies then estimate how much of the nutrient is needed to reach that endpoint in a group of people.
The choice of endpoint drives the result, and reasonable committees have chosen differently, which is why reference values vary between countries.
The published figure covers nearly everybody
Individual requirements vary, so what emerges from studies is a distribution rather than a single number.
The recommended intake is set above the average, at a level estimated to meet the needs of the large majority of healthy people in the group.
It is deliberately higher than what most individuals require, because the aim is to cover the upper part of the distribution. Consuming less than the recommendation is therefore not evidence of a shortfall.
Label values are a single set for a mixed audience
Labelling needs one number per nutrient, but requirements differ by age, sex and life stage.
Regulators resolve this by selecting a single reference for general labelling, usually derived from the highest requirement among the adult groups covered.
The percentage on a package is calculated against that fixed reference, so it does not correspond to the requirement of the particular person reading it.
An upper level exists and is separate
Alongside recommended intakes, committees set tolerable upper intake levels: the highest routine daily intake unlikely to cause harm in the general population.
The gap between the recommendation and the upper level differs greatly between nutrients, being wide for some and narrow for others.
Products listing percentages far above one hundred are not necessarily near an upper level, and knowing which case applies requires looking up the specific nutrient.
References assume a healthy population
These figures are built for healthy people. Illness, malabsorption, pregnancy, medication and some genetic variations shift requirements away from the reference.
Deficiency is established by testing rather than inferred from diet, and both the testing and any correction belong with a doctor rather than with label arithmetic.