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1. Read amount and unit together
A percentage without the declared amount is incomplete. Check whether the label uses milligrams or micrograms and whether the value refers to one serving or the maximum daily serving.
For example, 80 mg vitamin C corresponds to 100% NRV under the EU adult reference table. That statement does not describe individual blood levels or need.
2. Calculate the percentage
The formula is amount in the same unit divided by the reference amount, multiplied by 100. Convert units before calculating. One milligram equals 1,000 micrograms.
When two supplements contain the same nutrient, add the amounts first. A separate product, fortified drink and multivitamin can all contribute.
3. NRV versus upper limits
NRV supports nutrition labelling. A tolerable upper intake level, where one exists, serves a different risk-assessment purpose. The numbers are not interchangeable.
Individual medical advice may use yet another target based on diagnosis or laboratory results.