I ended up forgetting to pay my car property tax for 3 years in a row because I moved and didn't get the reminder notice in the mail. I think the late fee maxes out, but the first month is like 10% (or something similar) of the total. I believe they have to be paid in order to register your car. If your tags are expired, there may be a 30 day grace period before they charge a late fee ($30 I think) . Hope this helps, (source had to deal with this over the summer)