Product Expiration Tracker

Effective PAO is computed purely from PAO Months, Storage Conditions, and Product Type (line 15) -- Months Since Opened is never part of that formula. It is only used one step later, subtracted from the already-computed Effective PAO to produce Months Remaining (line 16), so a product's Effective PAO stays fixed no matter how long it has actually been open.

At the default settings, Months Since Opened actually moves Months Remaining by more per unit, not PAO Months. One extra month of PAO only adds Storage Conditions times Product Type worth of headroom -- 0.9 months at the default Room Temperature / Water-Based setting (line 15) -- because that multiplier attenuates PAO's effect rather than amplifying it. One extra month already open, by contrast, subtracts a full month directly with no multiplier of its own (line 16). So raising Months Since Opened by one month moves Months Remaining more than raising PAO Months by one month does, at these defaults.

The printed PAO number on the jar is only the starting point -- Storage Conditions and Product Type each apply their own multiplier before the calculator ever compares that figure to Months Since Opened (lines 10-15). A water-based serum stored in a warm, humid bathroom can have an Effective PAO barely half of an identical PAO powder kept cool and dark, since 0.65 times 0.9 is far smaller than 1.2 times 1.3.

Lifespan Used is Months Since Opened divided by Effective PAO, converted to a percentage and rounded, then explicitly capped at 100% (line 22). Once a product has been open longer than its Effective PAO, this output reports exactly 100% regardless of how many additional months have actually passed, which is also the point at which Status switches to "Expired — Replace."