The most common and most likely answer to this crossword clue is the 9 plus 4 letter word FINANCIAL YEAR
I've seen this crossword clue in The Guardian
F
I
N
A
N
C
I
A
L
Y
E
A
R
Buddy explains!
The straight part
We know that "accounts are based on it" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case accounts are based on it = financial year.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.