Late fee amounts? What to charge now that tenants don't seem to care about $50

[Toben B.]

When I started renting property I only charged a $20 late fee and the tenants didn't seem to care about this amount.  I changed it to $5 for every day late and this became a hassle to determine how many days late they were. I switched to a $50 late fee about 10 years ago and the tenants really tried to avoid it.   Lately it seems the tenants don't care about a $50 late fee and some will just pay $50 every month. 

Our local judge decided that any late fee above $25 is too much and will throw out the case over late fees. To avoid this most of the local apartments charge $100-$200 late fees, but in the event there is a court case with late fees, they will just drop the late fees when filing for a lawsuit for possession and back rent. 

What fee do you all charge for late fees? What is appropriate? FYI I live in a low rent area and my rents range from $575 to $1400. 

Thanks!