Notwithstanding the numerous studies conducted on stance-taking, the focus has been on the written discourse, particularly on academic writing. Little attention was paid to the phenomenon of stance in the spoken discourse, especially in casual conversations. This paper aimed at comparing the frequency of occurrence of (un)certainty as two main epistemic stance functions in two casual conversation registers of different levels of formality to investigate the influence of formality on stance functions. The research triangulation approach was used to analyze stance functions in two sub-corpora of the Corpus of Contemporary American English (COCA); TV/Movies, less formal, and the Spoken, more formal. The study showed a higher frequency of hedges and boosters in the Spoken sub-corpus. This finding demonstrated an influence of the level of formality on stance functions.