How much tongue weight should a trailer have?
For a conventional bumper-pull trailer, target 10 to 15 percent of the loaded trailer weight on the tongue. For a fifth-wheel or gooseneck, the pin weight target is 15 to 25 percent (fifth-wheels usually land 15 to 20 percent, goosenecks 20 to 25 percent). It is a range, not a single number. Below the band the trailer is prone to sway; above it you overload the hitch and the tow vehicle's rear axle. You change it by shifting cargo forward of or behind the trailer's axle, and the only accurate way to know your real figure is a tongue-weight scale or a CAT scale.
Does tongue weight count against my truck's payload?
Yes, and forgetting this is the most common towing overload. Tongue weight is a load the trailer places on the tow vehicle, so it comes directly out of the truck's payload, the 'combined weight of occupants and cargo' figure on the driver's door-jamb sticker, alongside your passengers and anything in the cab or bed. A 900-pound tongue weight uses 900 pounds of payload before a single person gets in. Many trucks hit their payload limit well before their tow rating.
What is the difference between tow rating, GVWR, GCWR, and payload?
Tow rating is the maximum trailer weight the vehicle is rated to pull. GVWR is the maximum loaded weight of the tow vehicle itself. Payload is the occupants-and-cargo share of that, from the door-jamb label, and tongue weight counts against it. GCWR is the maximum combined weight of vehicle plus trailer plus everything in both. They are separate ceilings, and the lowest one that applies to your setup is the one that governs; staying under the tow rating does not mean you are under payload or GCWR.
Does a weight-distributing hitch let me tow more?
No. A weight-distributing hitch uses spring bars to spread the trailer's tongue weight more evenly across the tow vehicle's front and rear axles, which restores steering-axle load and improves handling and braking. It does not raise your GVWR, GCWR, payload, or tow rating, and the tongue weight still counts against your payload. It makes a within-limits setup tow better; it does not make an over-limits setup legal or safe.
How do I measure my trailer's tongue weight?
The accurate ways are a dedicated tongue-weight scale, a Weigh Safe or similar scale-in-the-hitch, or a CAT/public scale (weigh the tow vehicle alone, then hitched, and take the difference on the relevant axles). A bathroom-scale-and-lever method exists for light trailers but is easy to get wrong. Because loading the trailer changes it, measure it loaded the way you will actually tow, and re-check if you move heavy gear.
Does this calculator tell me whether my setup is safe to tow?
No. It reports numbers and ranges: your target tongue-weight band, how much payload your load uses, and your margins against the ratings you enter. It does not and cannot tell you your rig is safe to tow. Safety depends on your specific vehicle, trailer, hitch, tires, brakes, loading, and conditions, and on staying under every one of your ratings at once. Weigh your loaded rig at a scale, read your ratings off the door-jamb sticker and owner's manual, and consult your vehicle or trailer manufacturer or a qualified professional.