Free Towing Capacity Estimate calculator with clear step-by-step results.
Towing capacity is the lowest of four independent limits, not the biggest number in the brochure. Gross combination mass minus the actual laden vehicle weight is often the binding constraint once the car is loaded, and the towbar or trailer axle rating can be lower than the vehicle's own limit.
GCM headroom
Headroom = gross combination mass rating - actual laden vehicle mass
Governing limit
Maximum towable = the smallest of GCM headroom, manufacturer limit, towbar rating and trailer axle rating
Towing limits are legally binding and safety-critical. Verify every rating from the vehicle plate, towbar plate and trailer plate, comply with licence category requirements, and have the combination weighed when loaded.
Gross combination mass caps the total of vehicle and trailer. Every kilogram of passengers and luggage is a kilogram unavailable to the trailer.
Guidance commonly suggests keeping the loaded trailer below 85% of the tow vehicle's kerb mass for stability, well below the legal maximum in many cases.