Learn Hardcore Serbian: Radije ostajem kod kuće.

Radije is an adverb meaning rather or preferably. In sentences like this, it often corresponds to English I’d rather... or I prefer to....

It expresses a preference between options, even if the other option is not stated.

Why is the verb ostajem and not ostati?

Ostajem is a conjugated verb form, while ostati is the infinitive.

In Serbian, a full sentence normally needs a finite verb, so you say ostajem = I stay / I am staying.

Here, ostajem is:

1st person singular
present tense
from the imperfective verb ostajati

So the sentence is built like:

radije = rather
ostajem = I stay / I’m staying
kod kuće = at home

What verb is ostajem from, and why is that form used?

Ostajem comes from ostajati, the imperfective partner of ostati.

This matters because Serbian often distinguishes between:

imperfective: ongoing, repeated, general
perfective: completed, single whole event

Using sounds natural for a general present preference or a current choice. It is not focused on the action being completed, but on the idea of .