Birkas Hamazon must be recited in the location where one ate.96 The following are the parameters of this halachah:
If one is eating indoors, the entire room in which he ate is considered the same location. Thus, he may bentch anywhere in that room even if the place where he ate is not visible from where he wishes to bentch (e.g., there is a divider in the middle of the room).97
If a disturbance arises and one cannot bentch in the room in which he ate, he may bentch in an adjoining room if he can see the place where he ate.98
If, upon reciting the berachah of Hamotzi, one was planning on bentching in a different room in the house, he may bentch in that room even when he cannot see the place where he ate if a pressing need arises (e.g., the place in which he ate is unclean and not fit for bentching).99
One who ate outdoors must bentch in the exact location where he ate. However, if a small disturbance arises, he may move up to four amos from his original location.100
One should not leave the location where he ate for an extended break,101 even if he plans to return to complete the meal.102 The Poskim provide two reasons for this halachah. 1) One might forget to return103 to complete his meal and bentch.104 2) Bread, being a significant food, requires that Birkas Hamazon be recited where it was eaten. This rationale also mandates not leaving that location before bentching.105 Accordingly, the following rules apply:
One can leave a meal before bentching if he intends to return immediately.106
One should not leave before bentching for an extended break, even with the intention of returning, unless he is leaving to fulfill a mitzvah that cannot be done later.107
If one leaves the meal (permissibly or not) with the intention of returning to complete it, he should not bentch before leaving. However, if he thinks he will be away for a considerable amount of time, he should bentch before leaving.108
One should not leave before bentching even if he plans on continuing his meal in another location. Instead, he should bentch before leaving and recite another berachah rishonah at his new location.109
If, however, the intention at the time of saying the berachah of Hamotzi was to continue eating in the second location, it is permissible to change locations before bentching.110 This is the appropriate practice for someone who wishes to join a tish or simchah at the end of the meal.
One who completes his meal and deliberately leaves before bentching111 must return to his original location to bentch.112 This obligation stands even if he has already traveled a great distance from his original location. However, if his food will be digested by the time he returns and he will not be able to bentch upon returning, he should bentch in his present location.113
Someone who deliberately leaves before bentching and neglects the requirement to return and instead bentches where he is, bedieved, fulfills his obligation of Birkas Hamazon and does not need to bentch again in his original location.114
One who mistakenly left his location before bentching115 should return to the original location to bentch. Under pressing circumstances, he may bentch in his present location.116
One is not required to return to the original location (whether he left deliberately or by mistake117) if he eats bread in the new location.118 Even eating less than a kezayis of bread in the new location is sufficient. However, he must eat bread and not any other type of food.119
96 Shulchan Aruch 184:1
97 Mishnah Berurah 184:1.
98 Ibid.
99 Ibid.
100 Mishnah Berurah 184:2.
101 Mishnah Berurah 178:34.
102 Rema 178:2.
103 Or he might delay his return until after the food he ate is digested and will no longer be able to bentch (Mishnah Berurah 178:33).
104 Rema ibid.
105 Bach cited in Magen Avraham 178:8, as explained by Shulchan Aruch Harav 178:4.
106 Mishnah Berurah 178:34.
107 Rema ibid. See Beiur Halachah, ד"ה עוברת who rules that one may leave for any mitzvah, even one that can be done later.
108 Mishnah Berurah 178:35.
109 Ibid. 178:33.
110 Ibid.
111 That is, he knew he was obligated to bentch in the location where he ate and decided not to follow the halachah.
112 Shulchan Aruch 184:1.
113 Mishnah Berurah 184:3
114 Ibid 184:4-5.
115 That is, he was either unaware of the halachah that one must bentch in the place where he ate or forgot to bentch.
116 Mishnah Berurah 184:7.
117 Mishnah Berurah 184:8
118 Shulchan Aruch 184:2.
119 Mishnah Berurah 184:9.