Adding different parts of a growing array.

I am building a financial model where a company earns a fixed % of revenue per month.

For example:
Company receives $10 in January but can only reconginze a certain % each month ie:
(Month1-30%, Month2-25%, Month3-14%, Month4-4%...etc..Month12-1%) so in 12 months it recognizes the full $10.

Now in February the company receives $12 and recognized the amount based on the above schedule.

I was wondering what is a good way to model out the monthly revenue keeping in mind that in in each month you have to take into account the previous month revenues?

ie: For March its going to $14*30%(assuming March they receive $14) + $12*25%(for February) + $10*14%(for January):

I am thinking of using an array but not sure how to add the previous months. Any insight would be great.

Thank you.