Shema: Sitting or Standing?
Question
Answer
Shalom!
Thank you for your question.
As a general rule, to is preferable to recite the Shema at Shacharit and Ma’ariv while sitting. This is especially true for the blessings recited before and after the Shema, as well, especially in the morning.
If one was standing while reciting the blessings before the Shema in the morning, one is permitted to sit for the actual Shema.
If one was standing while reciting the blessings before the Shema in the evening, one is not permitted to sit for the actual Shema.
One who is sitting when he began the Shema should not stand while still reciting the Shema. So too, one who is standing when he began the Shema should not sit while still reciting it.
In other words, one should not change one’s position while reciting the Shema. One who did so, nevertheless, fulfills the mitzva of Shema.
Source
OC 63 with commentaries