Character count mismatch between different word version

Hi

I just taking a character count using the word inbuild option, but I found different character count for the same document as listed below

Word 2010  -- 416116 character count

word O365  -- 405392 character count

Word web  -- 404756 character count

I tested the same word file in the above 3 version it showing different character count. Any one have face this kind of issue. please let us know

Thanks

Ganesh.R