'by end of ' vs 'by the end of'?


When do you use ‘by end of the year/next week/June/etc’ and when do we use ‘by the of the year/next week/June/etc.’?

Thank you very much.

If written in full it should always be ‘by the end of the …’
By end of… is an abbreviation (in a similar way as ‘today is Monday 25 April’ is an abbreviation of ‘today is Monday the 25th of April’).

But when do we use the full form and when the abbreviation?

Especially in business contexts I often see short forms that do not always comply with standard grammar, so I wonder if that abbreviation can be used…

As I said, if written in full it should be the long form.
Otherwise there is no reason why an abbreviation cannot be used.