How it works
The manufacturer’s Gross Combined Weight Rating (GCWR) is the most the tow vehicle and the loaded trailer may weigh together. Everything already in the vehicle uses part of that rating, so the weight left for the trailer is:
Real towing capacity = GCWR − curb weight − passengers − cargo
If you also enter the manufacturer’s maximum trailer rating, the calculator uses whichever is lower. A truck can have plenty of GCWR left and still be limited by its frame, hitch or cooling system, which is what the published tow rating reflects.
When you add a planned trailer weight, the result is shown against the 80% rule: below 80% of capacity is shown as OK, 80–100% as at the limit, and anything above capacity as exceeding it.
Worked example
A half-ton pickup has a GCWR of 15,000 lb and a curb weight of 5,500 lb. Four people weigh 500 lb together and there is 300 lb of gear in the bed.
- 15,000 − 5,500 − 500 − 300 = 8,700 lb of real towing capacity.
- 80% of that is 6,960 lb, a comfortable target for the loaded trailer.
- A 7,500 lb travel trailer would be inside capacity but above the 80% comfort margin.
How passengers and cargo shrink towing capacity
Same example truck (GCWR 15,000 lb, curb weight 5,500 lb). Every pound in the vehicle comes straight off the trailer you can pull.
| People + cargo in vehicle | Real towing capacity | 80% target |
|---|---|---|
| 0 lb | 9,500 lb | 7,600 lb |
| 300 lb | 9,200 lb | 7,360 lb |
| 600 lb | 8,900 lb | 7,120 lb |
| 900 lb | 8,600 lb | 6,880 lb |
| 1,200 lb | 8,300 lb | 6,640 lb |
| 1,500 lb | 8,000 lb | 6,400 lb |
80% rule chart
Quick reference for the comfort margin at common tow ratings.
| Towing capacity | 80% target | Headroom kept |
|---|---|---|
| 3,500 lb | 2,800 lb | 700 lb |
| 5,000 lb | 4,000 lb | 1,000 lb |
| 6,000 lb | 4,800 lb | 1,200 lb |
| 7,000 lb | 5,600 lb | 1,400 lb |
| 7,500 lb | 6,000 lb | 1,500 lb |
| 8,000 lb | 6,400 lb | 1,600 lb |
| 9,000 lb | 7,200 lb | 1,800 lb |
| 10,000 lb | 8,000 lb | 2,000 lb |
| 12,000 lb | 9,600 lb | 2,400 lb |
| 14,000 lb | 11,200 lb | 2,800 lb |
Other limits that can stop you first
Towing capacity is only one of several ratings. Any one of them can be the real limit:
- Payload (GVWR − curb weight): passengers, cargo and tongue weight all count. See the payload calculator.
- Hitch rating: the receiver, ball mount and ball each have their own limits. See the hitch class calculator.
- Rear axle rating (GAWR): printed on the door-jamb label. Tongue weight loads the rear axle heavily.
- Tire load ratings: on the vehicle and on the trailer.
Common mistakes
- Using the brochure maximum. That figure usually assumes a stripped-down vehicle with only a driver.
- Forgetting accessories. Bed covers, toolboxes, running boards, bigger tires and a weight distribution hitch all add weight.
- Using the trailer’s dry weight. Compare capacity with the loaded trailer, not the empty number on the sticker.
- Ignoring payload. Many trucks run out of payload before they run out of towing capacity, especially with heavy tongue weights.