Preservative Challenge Calculator

This calculator scores whether a planned preservative level matches a cosmetic formulation's microbial risk profile. Each preservative type carries minimum effective percent, maximum allowed percent, optimal pH low, and optimal pH high from a five-entry lookup table (lines 31-39). pH compatibility is a straight range check against those bounds (line 42). Concentration adequacy compares your entered percent to the type minimum (line 45), and exceeding the type maximum sets a separate over-limit flag (line 46). Microbial risk sums three capped contributions: water activity above 0.6 adds up to 40 points scaled from the excess above 0.6 (line 50); pH between 5 and 8 adds 30, below 5 adds 10, above 8 adds 20 (line 53); leave-on products add 30 versus rinse-off at 10 (lines 55-56). The total risk score caps at 100 (line 58).

Recommended preservative percent starts at the type minimum, scales by one plus risk score minus fifty over one hundred, then caps at the type maximum (lines 65-67). Gram weights multiply batch size by your percent and by the recommended percent (lines 70-71). Efficacy score is your percent divided by recommended, scaled by 80 and capped at 100, applied when pH is compatible, concentration meets minimum, and you are not over max (lines 75-76) — so exceeding the recommended level by 25% or more still reaches the 100 cap, it is not stuck at 80 — but forces zero for MIT on leave-on products regardless of concentration (line 77), and drops to 30 when concentration is adequate but pH falls outside range (lines 78-79). Batch size scales gram outputs only; it never enters risk or efficacy math.