Late fee question.

[Deb Smith]

when there's a late fee  policy of a % of the rent and a partial payment is made.  Say rent is $1500 and only $1000 is paid.  Is the % on the total rent or just the unpaid amount. 

Ex: say the fee is 10%   Rent is $1500 and tenant only paid $1000

Would it be $150 (the 10% of $1500 rent total  OR....

Would it be $50 ( the 10% of unpaid $500)