Did you know the manufacturers tow rating does not include the weight of passengers, cargo or aftermarket add-ons? Any weight you add to the tow vehicle reduces the tow rating by that amount. The tow vehicle also has a Gross Combined Weight Rating (GCWR). This is the maximum permissible weight of the tow vehicle and the trailer combined when fully loaded for travel.
Let's say for example that your GCWR is 8,500 pounds and your vehicle weighs 4,100 pounds when it's fully loaded for travel. 8,500 minus 4,100 equals 4,400. This means that the maximum fully loaded trailer weight you could tow is 4,400 pounds before you exceed the GCWR. There are numerous other factors to consider such as how much the hitch receiver is rated for, proper hitch work, trailer brakes and more.
This tip contributed by Mark Polk at RV Education 101