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- On Saturday night (Motzei Shabbat) in the fourth Bracha of Shmoneh Esrei (of Arvit) one should add in the paragraph of Atta Chonantanu which serves partially as Havdalah. 
- Even if one happened to say havdalah on a cup before praying arvit, he would recite atta chonantanu in the shemoneh esrei. 
- On Motzei Yom Tov (night of the conclusion of Yom Tov) one should say Atta Chonantanu in Shmoneh Esrei of Arvit/Mariv even if the Yom Tov is following by Chol HaMoed. 
If one forgot Atta Chonantanu
- If one forgot to say Havdalah in Shmoneh Esrei (Atta Chonantanu in Atta Chonen, the fourth Bracha) once one finished the Bracha even if one didn’t begin the next Bracha one shouldn’t go back to say Atta Chonantanu.  Additionally, one should not say it between atta chonen and hashivenu  or add it into shomeah tefilla. 
- If one forgot Atta Chonantanu and finished Shmoneh Esrei one doesn’t have to repeat Shmoneh Esrei, however, if one wanted to be strict on oneself one may repeat it. However, one not be strict upon oneself after having finished the Bracha to go back to the Bracha in order to add Atta Chonantanu. 
- If one didn't recite atta chonantanu, he may not do melacha until he recites havdalah or says "ברוך המבדיל בין קודש לחול" 
- If one anticipates that he will not have wine or something else that it is permitted to recite havdalah over, and he forgot atta chonantanu he must repeat shemoneh esrei.  However, if he remembered after saying Hashem's name but before finishing the beracha, he should recite "למדני חקיך" and go back to the beginning of the beracha. If not, he may recite it in shomea tefilla. As long as he hasn't taken his three steps back, he may return to that beracha. If he took the steps back, he must return to the beginning 
- If one forgot Atta Chonantanu and then mistakenly ate before making Havdalah one must repeat Shmoneh Esrei with Atta Chonantanu. 
- If one forgot Atta Chonantanu and one knows (thinks) that he will not be able to make Havdalah neither Saturday night nor Sunday then one should repeat Shmoneh Esrei to add in Atta Chonantanu. 
Cases of Tashlumin
- If one forgot to or mistakenly did not recite Mincha on Shabbat afternoon, see If one forgot to say Mincha on Shabbat afternoon on the Tashlumin page.
- If one forgot to or mistakenly did not recite arvit on Motzaei Shabbat, see If one forgot to say Arvit on Motzae Shabbat on the Tashlumin page
- When Yom Tov falls out on Motzei Shabbat (Saturday night) one is supposed to say VeTodienu in the Arvit/Mariv Shmoneh Esrei. 
- If one forgot to say VeTodienu one doesn’t have to repeat the Bracha or Shmoneh Esrei like Atta Chonantanu. However, if one ate before making Kiddish one has to repeat Shmoneh Esrei (like Atta Chonantanu). 
When Tisha B'av Falls out on Sunday
- For the laws of Atta Chonantanu when Tisha B'av falls out on Motzaei Shabbat/Sunday see When Tisha BeAv falls out on Sunday
- Shulchan Aruch 294:1, Yalkut Yosef Shabbat vol. 1 pg. 439, Kitzur Shulchan Aruch 96:1, Mishna Brurah 294:2. Gemara Berachot 33A says that this since it is the first beracha which discusses weekday matters it should be added there. The gemara also brings the reason that one needs knowledge in order to distinguish between Shabbat and weekday so we do havdala in that beracha.
- Mishna Brura 294:1
- S”A 491:1
- S”A 294:1,4. Yalkut Yosef Shabbat vol. 1 pg. 441 adds that this is true if one simply recited Hashem's name in the beracha but didn't finish the beracha
- Yalkut Yosef Shabbat vol. 1 pg. 441, Mishna Brurah 114:32
- Yalkut Yosef Shabbat vol. 1 pg. 441
- S”A 294:5
- Yalkut Yosef Shabbat vol. 1 pg. 441, Mishna Brurah 294:3
- Shulchan Aruch 294:2.
- Yalkut Yosef Shabbat vol. 1 pg. 441, Mishna Brurah 294:6
- S”A 294:1, Mishna Brurah 294:4. Yalkut Yosef Shabbat vol. 1 pg 442 adds that since there are opinions that say you would not need to repeat it, one should do repeat it but make it on condition that if he doesn't have to, that this will be a voluntary prayer
- S”A 294:2, Mishna Brurah 294:5
- S”A 491:2, 599:1
- Beiur Halacha 294:1 s.v. VeIm, Kaf HaChaim 599:3