Hi Elisey Ozerov. Good question! With calisthenics instead of aiming for a % of a rep max you would instead use different variations of an exercise to stay challenged within the 4–12 rep range depending on your goal.
For example, if you can easily do 12+ standard press ups you would try to do close grip press ups or feet elevated press ups instead, with the idea being to slowly working your way to harder and harder variations to keep you challenged within the desired rep range.
Essentially all you are doing is manipulating the load used by using increasingly difficult exercise variations instead of increasing the weight lifted as you would with weight training.
I hope this helps :)