If rent payment is past the 5th, a late fee will be added.

Literal

Rent [possessive-の] payment [subject-が] 5th-day [past-を過ぎる] [automatic-と], late-fee [subject-が] added.

Straightforward administrative language. 延滞料金 ('late fee') — 延滞 'delay/arrears' + 料金 'fee.' 加算される ('to be added') is passive of 加算する. The conditional と is the automatic/natural-consequence type: passing the 5th automatically triggers the fee.