Usually, it will work out to 15-20% of the total trailer weight. A good rule of thumb is to allow for 20% of the max GVWR weight rating, gives a little bit of wiggle room and margin of safety. most people will fill the trailer up close to max GVWR.
Our 10,141lbs GVWR fifth wheel usually weighs in at around 9400 - 9600lbs with 1/2 tank of water with a pin weight in the neighborhood of 1700 lbs, We have extra weight at the front, an Air Ride pin box is 150lbs and had 240lbs of batteries in the front bay, Thankfully the lithium will reduce that now.

I had an RV dealer once tell me no one loads their RVs up to GVWR. I responded, "you've never been married, have you?"

Ha!