I have this formula -

=RANK(S53,$S$53:$S$152,0)+COUNTIF(S$53:$S53,S53)-1

It is used for numbers in cells s53-s88. It works pretty much correct, but for some reason it will skip one number. Last week it skipped Rank 20, this week it is skipping rank 15.

Any ideas why it is doing this?