If You Said Al HaMichya Instead of Birchas HaMazon What Should You Do?
If after washing and eating bread you by mistake said Al HaMichya instead of Birchas HaMazon, are you yotzei or do you now need to say Birchas Hamazon? Rav Yechiel Michel Stern says in his sefer Birchas HaNehenin (Perek 1) that if you only ate a Kezayis and did not eat "Kdei Seviya" since your Chiyuv Birchas HaMazon is only MiDirabanan, you are yotzei with Al HaMichya and do not need to say Birchas HaMazon.
If you ate Kdei Seviya and are obligated to say Birchas HaMazon Min HaTorah, in this case there is a Machlokes HaPoskim. Rebbi Akiva Eiger and the Shulchan Aruch HaRav and others (see also Mishna Brura 191:1) hold that you are yotzei your Chiyuv Birchas HaMazon even if you only said Al HaMichya. The Bach and Elya Rabba among others disagree and say that you are not yotzei and you need to say Birchas HaMazon. Rav Stern paskens that since we say "Safek Brachos L'Hakel", we are lenient with brachos that are in doubt, since it is a Machlokes you should not say Birchas HaMazon.
As an interesting footnote he brings the Maharshag who says since the gemara says whoever does not mention "Bris" and "Torah" in Birchas HaMazon is not yotzei, therefore Al HaMichya which does not include these two things cannot work in place of Birchas HaMazon. Rav Stern answers that this gemara says you are not Yotzei if in Birchas HaMazon you do not say Bris and Torah. However since Al HaMichya does not include them in the nusach, in a case where Al HaMichya would help instead of Birchas HaMazon it is not considered as if you skipped Bris and Torah.
Important Note: We try to convey the Tshuva to the best of our ability. We admit that our understanding may not be accurate. Please also understand that this Tshuva may not be the final word on this topic. One should consult a Rav before drawing any conclusions.