If one comes late to maariv and missed kriyas shema but says shemoneh esrei with the tzibbur, when does he count sefirah? Does he say shema first because it is deoraysa and tadir or does he count sefirah with the tzibbur?
If a person is concerned for forgetting to count the Omer, it is permitted to count before reciting the Shema.
If a person is not concerned for this, he should say Shema first – because it is de’oraisa and because it is tadir.
See Magen Avraham 489:7; Shulchan Aruch Ha-Rav 489:16; Mishnah Berurah 489:18; see also Biur Halachah 489 (s.v. achar tefillas).
Siddur Derech Chaim explains that this is because of concern for forgetting to count the Sefira.