There are 3 Additions into our Birkat Hamazon:

1. On Shabbat - we add the paragraph of “Retzei”

2. On Yom Tov, Rosh Chodesh and Chol Hamoed - we add “Yaaleh V’Yavo”

3. On Chanukah and Purim - we add “Al HaNisim”

General Rule: The rule as to what to do if one accidently forgot these additions – is quite simple. First, you need to decide if there was a chiuv (obligation) to eat a bread meal. If there was a chiuv to eat a bread meal, then you would need to repeat the bentching. If, however, there was no chiuv to eat the bread meal then you wouldn’t need to repeat the bentching.

1. Shabbat and Yom Tov

On Shabbos and Yom Tov, there is a chiuv to eat 2 bread meals: One at night and one during the day. Therefore if one forgot the addition for either of these two meals – he would need to repeat the entire bentching.  Moreover, if one is unsure whether he said the addition or not – he would need to repeat the entire thing again.

Regarding the 3rd meal on Shabbat (Seudat Sheleshit or Shalosh Sheudos), since there are opinions that one doesn’t need to eat bread at that meal – one would not repeat the bentching if he forgot the addition. And, in regard to Yom Tov, this is certainly true – since everyone holds one doesn’t need to eat a third bread meal on Yom Tov.

2. Rosh Chodesh and Chol Hamoed

Since there is no chiuv to eat a bread meal on these days – one would NOT repeat if he forgot the additions.

3. Chanukah and Purim

Likewise, since there is no chiuv to eat a bread meal on these days – one would NOT repeat if he forgot the additions

4. What If’s

• If one begins a meal on any of these days when one would need to insert an addition – but his meal carried on past the end of the day and into the next day – he would still add the insert.
• If one started his meal on a normal day but right before one of these days and carried into the special day – As long as he ate 1 kazayis of bread after the new day began – he would still add the insert.

So we see that it works in both direction, however a problem arise when we combine the two into one case:

• If one extended his Third Shabbat meal beyond Shabbat into the next day and it happened to be a Rosh Chodesh on that Motzei Shabbat – we initially advise the man not to eat bread after sunset (shkiya). The reason is because it would be contradictory if the man where to recite both a Retzei and Yaaleh V’Yavo in the same bentching when the Retzei comes from Shabbat and the Yaaleh V’Yavo comes from Sunday!

Bedieved, if one ate a kazayit of bread both before and after sunset – some advise to only say Retzei while others say he should insert both Retzei and Yaaleh V’yavo. One should consult a local orthodox rabbi for a definitive ruling.

5. Women

There is one crucial difference for men and women. Women do NOT have an obligation to eat two bread meals on Yom Tov and if they forgot – they would not repeat the birkas hamazon.

6. Midway Corrections

Now this can get complicated, so let’s organize it by 4 places of realization:

1a. If one realize his omission before he said Hashem’s name in the bracha, “Baruch Ata Hashem Boneh Yerushalim (Amen)”

1b. OR if he said Hashem’s name but only Hashem’s name and not the next word of “Boneh”, he can conclude the bracha “Lamdeni Chukecha” and then…
He can insert Retzei or Yaaleh V’yavo right then and there – and then continue from U’vanei (or from V’Tivne for sephardim)

2. If one finished the 3rd bracha but did not yet begin the 4th bracha, with the word, “Baruch”
You can insert a single short and unique bracha for these situations right then and there and then continue as normal (hopefully these brachot can be found in your siddur and hopefully one day I’ll have them online as well)

3. If he began the 4th bracha but only said the first 6 words, until the word “HaOlam”
He can cleverly switch over to the single short and unique bracha one is supposed to say in these situations.

4. Beyond that – I’m sorry, but you’ll need to repeat the entire thing

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