There are as many different opinions as there are people when it comes to weight carrying ability
For a 20% rule we go 950/100 x 20 so 950/100 = 9.5 the multiply by 20 = 190 for weight of rider and tack.
But depending on the build of your horse, and who you ask, and the sort of riding you are doing, some would argue 25% is OK. Now that math is easy, just divide 950 by 4 = 237.5
But the trouble with those simple calculations is that it takes no account of what weight your horse should be, and a fat horse can carry LESS weight than a fit one.
This formula works better as it takes into account the amount of bone your horse has---
Measuring a horse's cannon bone is used by some in determining the approximate weight a horse can carry. A measurement is taken around the circumference of the foreleg, just below the knee.
Add together the weight of the horse plus the rider and tack, and divide this sum by the cannon bone circumference measurement.
Then divide that result by two.
A number between 75 and 85 is good.
If the number is over 85, you probably need a larger horse.
When it comes down to it the only one who can tell you if you are to heavy is your horse