Let us first clarify a few things about the minhag of machatzit hashekel before dealing with specifics. There is a mitzva from the Torah[2] to donate a half shekel every year (during the month of Adar) for the upcoming year’s public sacrifices.[3] While this does not apply now,[4] a minhag has developed to give a donation in memory (zecher) of the practice. (It must be clear that it is only a zecher, as an attempt to make a real machatzit hashekel would produce hekdesh[5] coins that must be used only for the Beit HaMikdash.) Notably, this old minhag[6] was not cited in such basic sources as the Rambam and Shulchan Aruch, but it is cited in the Rama.[7] At some point in history, Sephardim also adopted the minhag.[8]
Given that the original mitzva was to donate a half-shekel to the Beit HaMikdash, it might have been expected that one would give a single half-shekel coin as a zecher to the machatzit hashekel.[9] However, the Torah[10] mentions the word “teruma” three times in that context (in the first year of donation, when the Mishkan was being assembled, there were three donations), and the Rama consequently says that we should give three such coins. The standard practice is to give half denominations of the local currency; the Rama mentions specific coins appropriate in his time in different places. In our time, the Israeli half-shekel and the American half dollar are appropriate, in the respective countries. Since the classical coins from the Beit HaMikdash’s times were made out of silver, there are shuls that provide old half dollar coins, which contain a significant amount of silver, but this is not a real requirement. These shuls usually allow people to buy the special coins for whatever price they like, and, of course, they donate the coins back to the “pot.”[11] Some poskim suggest that one should give the value of a Biblical half shekel (approximately 10 grams of silver[12]).[13] Many people take the opportunity to make more significant donations. (Anything above the minimum amount, according to the various opinions, may be taken from ma’aser kesafim money.[14])
The Rama says that only men above the age of twenty are required to give the machatzit hashekel, as the pasuk[15] seems to indicate.[16] In contrast, the Tosafot Yom Tov[17] says that involvement in the donation for the korbanot applies to all male adults, as the mention of a twenty-year old minimum concerns a one-time donation also referred to by those p’sukim. The Mishna Berura[18] notes that it is customary to give even on behalf of women and young children. A reasonable compromise is for men over twenty to give the larger amount (equivalent to the Biblical half shekel) and others to give the smaller amount (equivalent to half of the local currency),[19] since it is not logical to build stringency on stringency regarding this minhag.
There are various opinions about when the optimal time is to give the machatzit hashekel. Although the Mishna Berura[20] cites an opinion that it is done before the morning reading of Megillat Esther, the more prevalent minhag is to give it before (or after) Mincha the day before Purim. This means that it is usually done on Ta’anit Esther. Indeed, the Kaf HaChayim[21] says that the Mincha of the fast is the appropriate time to give money that goes to tzedaka. His implication is that even Jerusalemites, who observe Purim the day after everyone else, should give the machatzit hashekel on Ta’anit Esther. However, the more prevalent practice seems to be for Jerusalemites to give it at the Mincha before their Purim (on the day of Purim observed outside of Jerusalem), except on a Purim Meshulash year,[22] when they too give it on Ta’anit Esther.[23]