- Question: Why doesn’t Tosefes Yom Tov, taking on Yom Tov early in regards to prohibiting yourself from doing melacha before sunset, not contradict the 49 complete days of the Omer but saying kiddush and maariv before nighttime does?
A. The Mishna Berura (494:1:1) says that maariv should be pushed off to later on the first night of Shavuos until the stars come and it is completely night so that the days of the counting of Omer will be 49 complete days.
B. The Pri Megadim says this applies to saying kiddush also, if one would eat first then Daven maariv in a set minyan or for a woman who is alone and is not davening maariv.
C. Rav Nosson Karelitz says one can accept upon himself “Tosefes Yom Tov” because that doesn’t take away from the completeness of 49 full days it is just that one cannot do any melacha because he took upon himself Tosefes Yom Tov.
Answer: Davening maariv or saying kiddush is an action which actively shows they are moving on to the next day so if done earlier they are not completing the 49 days of counting. Whereas refraining from doing malacha is passive, all it is taking a vow not to do any work for a certain time period for the sake of honoring the Yom Tov but it does not show that they are ready to move on to the next day. (See footnote 1 and 2 in Dirshu there.)