Horner's rule for polynomial evaluation
I suppose you can use .reversed() or  .asReversed() to reverse the list of coefficients and iterate over it, without working with the indices:

coefficients.asReversed().forEach {
    result = (result * x) + it
}


Also, you can use the functional idiom of fold/reduce, and replace iteration with folding the list (here, .foldRight(...) is used to fold the collection from its end):

val x = 3
val result = coefficients.foldRight(0) { it, acc -&gt; it + acc * x }