I would guess that a late payment is a calculation based on the amount of the original loan. For example, if you loan someone $500 and they pay back $50 a month, then a late payment might be $20. If you loan another person $5000 and they are paying $100 a week, then a late payment of maybe $30 would be more appropriate.
If you do in fact use a calculation of some sort to determine the late payment, then you wouldn't want to store it anywhere -- calculate it on the fly. If on the other hand you have a set late fee that may be different for each loan, then storing it in the payment table is fine. If the late fee is the same regardless of the loan type or amount, then just set it as a constant and don't store it in the table at all.