Hosafos

Yaaleh Viyavo

• During davening. If you forgot to say Yaaleh Viyavo during Maariv and remembered after saying Hashem’s name at the end of the berachah, do not go back to repeat it.
• If you forgot to say Yaaleh Viyavo during Shacharis or Minchah and remembered after saying Hashem’s name at the end of the berachah, finish the berachah and say it before Modim. If you already began saying Modim, go back to Retzei. If you already said the second Yihiyu leratzon, go back to the beginning of Shemoneh Esrei.
• If you forgot to say Yaaleh Viyavo during Shacharis and only remembered after davening Musaf, do not repeat the Shemoneh Esrei of Shacharis.
• If you forgot to say Yaaleh Viyavo during Minchah and only remembered at night, daven Maariv twice, once for Maariv and the second time as a voluntary tefillah. However, since it is no longer Rosh Chodesh, do not say Yaaleh Viyavo during either Shemoneh Esrei. Say Atah Chonantanu during the first Shemoneh Esrei, but not during the second.
• All the above also applies if you are unsure whether you have said Yaaleh Viyavo.
• When bentching. If you remembered Retzei but forgot to say Yaaleh Viyavo and remembered before starting the berachah of Hatov vehameitiv, say the added paragraph for Rosh Chodesh printed in the bentcher or siddur. If you remembered after starting that berachah, do not go back.
• If you forgot to say both Retzei and Yaaleh Viyavo and remembered before starting the berachah of Hatov vehameitiv, say the added paragraph that combines Shabbos and Rosh Chodesh printed in the bentcher or siddur. If you remembered after starting that berachah (even if you just said the word “Boruch”), go back to the beginning of bentching.
• When repeating bentching due to forgetting Retzei, say Yaaleh Viyavo as well, even if you said it the first time.

Atah Yatzarta

• If you said Tikanta Shabbos instead of Atah Yatzarta and have not yet finished Shemoneh Esrei, go back to Atah Yatzarta. If you have already finished Shemoneh Esrei, repeat Shemoneh Esrei and say Atah Yatzarta.