Motorhome MAM explained simply: it is the heaviest your van is allowed to be on the road. Mass in Service versus MAM is the usual mix-up — one is a plated cap, the other is a paperwork empty-ish figure. Payload meaning is the gap between that cap and a real empty weight.
MAM (Maximum Authorised Mass)
The heaviest your van is allowed to be on the road. On the VIN plate. Same idea people call GVW.
Go over MAM → not legal. No “small margin” in law. We don’t invent a MAM; you read it from the plate.
Mass in Service (often on the V5)
A standard empty-ish figure from paperwork — not always today’s empty van. Useful as a starting point; a weighbridge beats it.
Our calculator treats V5 Mass in Service carefully and labels it — don’t mix it up with a full loaded weight.
Payload (what you can add)
Rough idea:
Payload ≈ MAM − empty weight
Empty weight should be a real empty weighbridge ticket when you can. Then people, water, gas, battery, and kit eat that payload. Axle limits still apply on top of the total — see front and rear axle weights.
Licence catch
If your licence is only category B (up to 3500 kg) and the van’s MAM is higher, that’s a licence problem — not something a calculator can waive.