Generally, you are correct - for "pay per profitable period" billing, customers are not charged until and unless your total Model Account profit exceeds the subscription charge (and is above any previous high-water mark).

However, my answer is complicated by the fact that there is a $100 minimum profit requirement before charging, to eliminate uncertainty and bad feelings about rounding, data/time granularities of equity calculations, etc. So I'm not sure if the very small numbers in your example ($22, $15, $30) are meant simply to illustrate your question clearly, or if they are meant as the real and specific numbers you are asking about.

As a general rule, your algorithm for billing is correct (billing happens after subscription cost is exceeded) but in real life billing won't take place if a system ekes out a $30 Model Account profit.

Thanks for the explanation, Matthew.

Can you give an example here about the "a $100 minimum profit requirement" based on a system which charges $22 for a profitable week?

And, for that system, if the provider got $20 profit for each week in 5 consecutive weeks, would subscribers be charged for the 5th week?

Thanks again