The success rate of projects in a call expresses what proportion of submitted applications receive support. It is essential to understand that meeting the conditions does not guarantee approval: if demand exceeds the allocation, projects are ranked by score and supported from the top down until the money runs out. The chances are therefore influenced by the ratio of the allocation to the number of applicants, the strictness of the conditions, which filter out some applicants, and scoring bonuses, for example for a less developed region or for cooperation. It can be estimated before submission: look at the results of previous rounds of the same scheme, the number of applications submitted and approved, and the score threshold at which the call stopped. If your project does not even come close to the threshold, it is cheaper to adjust the plan or wait for the next round than to submit blindly.
See also: Evaluation criteria, Allocation, Request for review of a decision.