The percentage or number of affordable housing units required per development varies widely based on local regulations, housing policies, and the specific needs of a community. Some regions might mandate that a certain percentage of new developments be set aside for affordable housing (e.g., 10% or 20% of units), while others may have incentives or voluntary schemes in place for developers to include affordable units. It's essential to consult local planning regulations or housing policies to determine specific requirements or guidelines in a particular area.