Supplement Interaction Calculator

This calculator looks up pairwise interactions among five supplements — vitamin D, iron, calcium, zinc, and magnesium — and reports an interaction level (0 none to 3 significant), an absorption impact percentage, and whether the pair should be taken apart. The pair you choose is everything: the engine holds a fixed interaction matrix, so Supplement A and Supplement B jointly select one row. Iron plus calcium is the worst pairing in the table, rated significant with a 50 percent absorption reduction; iron-zinc and calcium-zinc are moderate at 30 and 25 percent reductions. Two pairs are actually synergistic — vitamin D with calcium adds 10 percent to absorption, and vitamin D with magnesium adds 5 — and picking the same supplement twice always returns zeros, since a supplement does not interact with itself.

The Timing input only matters when the impact is negative: taking a competing pair two or more hours apart retains 30 percent of the absorption penalty (the number is the penalty scaled down, rounded), and it leaves positive or zero impacts untouched. Recommended Timing is a threshold read of interaction level — any pair rated 2 or above is flagged for separation regardless of what you enter for Timing. The matrix covers only these five supplements; dose sizes, food co-ingestion, and medications are outside the model.