Monthly cohort engine
Time dynamics matter. A flat annual rate would imply revenue arrives uniformly across the year, which doesn’t match how a WhatsApp list actually grows. The engine builds a per-month cohort of new opt-ins, ages each cohort forward, and applies churn to the cumulative stock so the numbers respect the fact that subscribers decay.
Each channel’s rate is a two-stage funnel: first, a fraction of the channel’s volume clicks through to WhatsApp (scans the QR, taps the link, etc.); second, a constant 90% of those click-throughs actually opt into the list. The per-industry click-through rates are tabulated below; the 90% opt-in is a global constant.
Channels split into two families. Recurring channels (online sessions and in-store walkthroughs) contribute the same monthly opt-in pool every month — they refresh organically. Finite stocks (email list, SMS subscribers, social followers) opt in once and then taper off; the engine spreads each channel’s annual opt-in pool across the year with a 60.00% / 25.00% / 10.00% / 5.00% decay tail (M1 / M2 / M3 / M4+ flat).
A constant 2.00% monthly churn is applied to the cumulative subscriber stock. This is a deliberate model commitment rather than a slider.