By how many percent(approximately) can my CommonApp essay and recommendation letters affect my chances of getting in?

Roughly your essay and letters combined account for 25% of your application. This doesn’t mean that a bad essay reduces your admissions chance by 25%; you can’t really calculate how much they factor into whether you are rejected or accepted. It’s not an exact science, but they are important to make sure to do your best.

It's not quite that simple, especially for schools in that very competitive range (sub-30% acceptance rate). At those schools, essays are the final differentiating factor between equally qualified students. If a school admits 3 out of 10 students like you (e.g., you're an average applicant), then your essay needs to be better than 7 of those theoretical 9 other students.

So, in short, a bad essay will absolutely tank your chances at a school like that. An extremely good one can give you great chances, as long as the rest of your application is up to par. An average essay—well, it depends on who you're competing with then, and how good the other applicants are.

For those schools it is around 30% iirc but assuming they are not horrible or amazing it will come down to the more numerical aspects of education gpa SAT etc.

Amazing ones can make you get advocated for my a admission reviewer and that really helps but assuming the essay avoids cliche you don’t bribe them you don’t do a stupid “cute” essay. An admission person I talked to said someone wrote the essay in binary yeh not great. Essays really don’t hurt you as long as you talk about your positive personality.

Recommendations long as the teacher doesn’t say he’s horrible and can provide a anecdote for you you should be strong in this area.

Hope this helps!