value for donation

[pedro fonseca]

for each product, 80% of value (price - wholesale_price) go donation.

is necessary create a new field and value for database?

example:
wholesale_price : 10€
price: 15€

value: 5€

80% this value: 9€ (for donation). This 9€ appear in FO (page product)

this 80% i define in Back Office. At momment is 80%, but in future i think to be 90%.

need sugestions and ideas