How much can I tow? GCM calculator

Find the heaviest trailer your vehicle can legally pull as it's loaded today, and which limit stops you.

Short answer Your real towing limit is the lowest of four numbers: the towing capacity, GCM minus your loaded vehicle's weight, the trailer weight that would push the vehicle over GVM through the towball, and the trailer weight that would exceed the maximum towball download. On many utes the GCM figure is the one that bites.

Start from your vehicleOptional. Fills in the manufacturer's figures, which you can still change.

Vehicle not listed? Enter the figures from its compliance plate or owner's manual below. See all vehicles.

Your vehicle's limitsFrom the compliance plate, owner's manual or manufacturer specs
How your vehicle is loaded

The formula

Work out each of these, then take the smallest:

Towing capacityGCM − loaded vehicle(GVM − loaded vehicle) ÷ towball %Maximum towball download ÷ towball %

Add the towbar's rating to the list if it's lower than the vehicle's towing capacity. Aftermarket towbars are sometimes rated lower than the vehicle.

Worked example

The example values describe a ute with a 6,000 kg GCM, 3,200 kg GVM, 3,500 kg braked towing capacity and 350 kg maximum towball download. Loaded with a canopy, drawers, two people and camping gear it weighs 2,850 kg.

  • Towing capacity: 3,500 kg
  • GCM: 6,000 − 2,850 = 3,150 kg
  • GVM: (3,200 − 2,850) ÷ 10% = 3,500 kg
  • Towball download: 350 ÷ 10% = 3,500 kg

The smallest is 3,150 kg, set by the GCM. That's 350 kg less than the towing capacity, and the only way to get it back is to take weight out of the vehicle. Every kilogram removed from the ute adds a kilogram to the trailer you can tow, up to the 3,500 kg towing capacity.

Turning it around: how much can I load the vehicle?

If you already own the trailer, flip the question. Your loaded vehicle must weigh no more than GCM minus the trailer's weight, and no more than GVM minus the towball download. For a 3,000 kg caravan with 300 kg on the ball and the limits above, that's 6,000 − 3,000 = 3,000 kg and 3,200 − 300 = 2,900 kg. The vehicle must stay under 2,900 kg. Use the payload calculator to see what that leaves for people and gear.

Common questions

Why can't I tow my vehicle's full towing capacity?
Because the vehicle and trailer together must stay under the GCM. If GVM plus towing capacity adds up to more than the GCM, every kilogram you load into the vehicle comes off the trailer you can tow once you reach that point.
How do I work out the maximum trailer from GCM?
Subtract what your loaded vehicle weighs (unhitched) from the GCM. Then compare that with the towing capacity and the towbar rating. The lowest figure is your limit.
What towball download percentage should I use?
Use your own measured figure if you have one. If not, 10% of the trailer's weight is a common planning figure. Published guidance ranges from about 5% to about 15%.
Does a GVM upgrade let me tow more?
Not necessarily. A GVM upgrade done before the vehicle is first registered can come with a changed GCM, but many upgrades raise GVM without raising GCM, so extra load in the vehicle still reduces what you can tow. Check the upgrade's paperwork for its GCM and towing figures.

Sources

Rules checked against these sources on 12 October 2026. See rules, sources and method.

Check your own plates. This calculator uses the numbers you enter. Your limits come from your vehicle's compliance plate and owner's manual, your trailer's plate and your towbar's rating. The only way to know your real weights is to weigh the loaded rig at a public weighbridge.