M(t,N) = M0 [1 - t / (E-N)]
where M0 is your "raw" mark, t is the number of days you are late ("days" start and end at midnight for this calculation; an integer value will be used), N is the number of people who turn in their papers late, and E is the (integer) number of days between the due date and the final exam. Thus (for example) if there are 17 days between the last class and the final exam but 10 people turn in their papers late, there is no point in turning in your paper a week late because it will receive zero marks. The intent of this formula is to ensure that I have time to give each paper the attention it deserves without running past the exam date, after which I must mark exams as quickly as possible to ensure that graduating students get their marks in time for graduation.