Doubt if one made Birkat HaMazon

From Halachipedia
  1. If a person ate bread but is in doubt whether he said Birkat HaMazon, it’s preferable to wash again, make another hamotzei and have a kezayit so that will be surely obligated in making Birkat HaMazon. [1]
  2. If a person ate a kezayit of bread but isn’t full, and now is in doubt whether he said Birkat HaMazon he shouldn’t go back and make Birkat HaMazon. [2]
  3. If a person ate bread and is full but is in doubt whether he said Birkat HaMazon, one must go back and say Birkat HaMazon. According to Ashkenazim, one should say the entire Birkat HaMazon, whereas according to Sephardim, one should only say the first 3 Brachot. [3]
  4. If a person ate bread and is still thirsty becuase he didn't drink enough during the meal and now has a doubt whether he said Birkat HaMazon, some say he should repeat Birkat HaMazon and some say not to repeat it. Cite error: Closing </ref> missing for <ref> tag

References

  1. Mishna Brurah 184:15 comments that a Yireh Shamayim should make sure to wash again, make hamotzei and have a kezayit in order so that one will be surely obligated in Birkat HaMazon. So rules Kaf HaChaim 184:15.
  2. Mishna Brurah 184:15 writes that according to many ריאשונים only if one ate and is full is one chayav deoritta, therefore if one only had a kezayit and is in doubt whether he said Birkat HaMazon one shouldn’t go back and say it out of doubt, rather it’s preferable to wash again, make hamotzei, eat a kezayit and make Birkat HaMazon. So rules Yalkut Yosef (Brachot 286).
  3. S”A 184:4 rules that if a person is in doubt whether he said birkat hamazon he has to go back and say it since birkat hamazon is deoritta we don’t apply the general rule of Safek Brachot Lehakel. Mishna Brurah 184:13 comments that when one repeats the benching one must say all four Brachot even though the forth one is only derabbanan so that people don’t disregard it’s importance. However, the Sephardic achronim including the Kaf HaChaim (184:15) and Yalkut Yosef (Brachot pg 282) argue that since the forth Bracha is derabbanan we apply the rule of Safek Brachot without concern for a remote possibility of those who will degrade the forth Bracha.