Length of the permit

 If you are an intern in the green sector, you can obtain a residence and work permit for up to 18 months, but not longer than the duration of your contract.
However, if you supplement your internship with a stay at a Danish agricultural school or technical school for a duration of 6 to 8 months, you can obtain a total residence permit of up to 24 months.

If your internship is extended, you must apply for an extension of your residence and work permit. It is important to do this before your permit expires. If you submit the extension application on time, you are allowed to stay in Denmark and continue your internship while the application is being processed, even if your residence permit expires. 

A residence permit as an intern can only be valid until the expiration of any approved training place. If the training place approval of your internship host has a shorter validity than the otherwise possible residence period, your residence permit will be shortened.
This means that the length of your residence permit will be shorter than it could normally be. Once your internship host has obtained a new training place approval, you can apply for an extension of your residence permit.