Task success — How do we establish how much to deduct from the total TPI (task performance indicator) when measuring the success score of a task?

Does anyone have experience in measuring task success with a TPI score?

As an example I can give measuring task success on a travel website and example tasks would be:

• Search for a holiday destination I have in mind
• Filter by date availability
• View what's included in the deal.

If a maximum score for a task is 100, how do we establish how much to deduct from that depending on the types of struggles a user might have when competing it? Is there an universal formula for this?