If someone asks his friend, at a time when it is permissible to count, “What is today’s Omer count?” the friend should not answer, “Today is day such-and-such in the Omer,” unless he has already counted with a blessing. After all, if he says this, he will already fulfill his obligation to count and will be unable to recite a blessing over that day’s count. Rather, one should answer, “Yesterday was day such-and-such in the Omer” (Sh.A. 489:4).
If one tells his friend which day it is in the Omer while having specific intent not to fulfill his obligation, he may count later on with a blessing. If the day’s count is made up of both days and weeks [i.e., after day six] and one tells his friend the number of days [without mentioning the weeks], he may count later on, be’di’avad, with a blessing. Since he did not count in the normal fashion, mentioning both the days and the weeks, he has made it clear that he did not intend on discharging his obligation of the mitzvah with this response (M.B. 489:22).
Before reciting the blessing, one should remind himself mentally what day it is in the Omer (see Sh.A. 489:6, Sha’ar HaTziyun 37). If someone in unsure whether today is day nine or ten [for example], and there is no one available to ask, he should say both numbers, and thus fulfill his obligation either way. However, the poskim debate whether or not to recite the blessing [in such a case]. Some say that one may recite a blessing only over a clear and definite count. Others maintain that one may recite a blessing over a doubtful count, because the person knows for sure that one of the numbers is correct (see Piskei Teshuvot 489:17). In practice, the blessing should be omitted since there is a doubt regarding the matter.