This may sound like a dumb question, but I was comparing the calcium content in almond milk (45% of daily value per serving) vs. cow milk (30% per serving) and ran into this problem. It appears almond milk has 1.5 times the amount of calcium per serving than cow milk (correct me if I'm interpreting the percentages wrong). Does that mean that there is 50% more calcium in almond milk or just 15% more? The serving size is the same for both milks.
It seems like it would be 50% more since it's 1.5x as much calcium, but since we're dealing with percentages already do you just subtract 30 from 45?
I guess my general question is, when comparing two percentages, do you simply subtract one from the other or do you divide one from the other to get the ratio?
Almond milk contains $50\%$ more calcium than cow milk. And, almond milk also contributes $50\%$ more towards your daily need than cow milk does, as $0.45 = 1.5 \times 0.3$.
However, almond milk contributes $15$ percentage points more towards your daily need than cow milk does.
That is, there is a specific terminology to address the ambiguity you observe.