“On the first of Adar, announcements are made concerning the payment of shekels” (Mishnah, Shekalim 1:1). In Temple times, a half-shekel was collected from every person yearly to pay for the communal sacrifices. This collection took place during the month of Adar.
It is a Jewish custom to give charity during the month of Adar as a remembrance of this half-shekel.
When to give — The custom is to give this money after Mincha on Ta’anit Esther. One may give it at any time between Rosh Chodesh Adar and Rosh Chodesh Nissan.
Who should give — “This is what everyone who is entered in the records shall pay: A half-shekel by the sanctuary weight . . . everyone who is entered in the records from the age of twenty years and up shall give the Lord’s offering” (Shemot 30:13-14). The original obligation was limited to males over twenty years old who were counted in the census. In practice, the custom has been to give on behalf of all — men, women, and children — because all need the forgiveness granted through the halfshekel. As we read in Parashat Shekalim, “It shall serve the Israelites as a reminder before the Lord, to atone for your souls” (Shemot 30:16). There are those who are accustomed to give on behalf of the fetus of a pregnant woman as well.
How much to give — The half-shekel of Biblical times is the equivalent of ten grams of pure silver (which nowadays is worth approximately 13 New Israeli Shekel). Ashkenazim follow the custom recorded by the Rema (Orach Chaim 694) to give three coins, each of which is half of their country’s currency (in Israel today this would be one-and-a-half New Israeli Shekel). The source for giving three coins is the triple repetition in the verse at the beginning of Parashat Terumah, “Tell the Israelites to bring Me offerings. From every man that gives it willingly with his heart you shall take My offering. And this is the offering which you shall take from them . . .” (Shemot 25:2-3).
There is a special Israeli commemorative coin that is minted of pure silver that has the worth of the original half-shekel. This coin can be placed near the special pushke (collection box) which will be in shul on Ta’anit Esther. One who wishes to do the mitzvah in the most ideal way and give this coin can acquire the coin from the pushke in exchange for an equal amount of money. After acquiring it, he can then donate the coin by returning it to its place near the pushke.