Positive commandment · Mitzvat Aseh #171 of 613
To give a half-shekel each year
ליתן מחצית השקל בכל שנה ושנה
The verse · Shemot 30:13
זֶה יִתְּנוּ כׇּל־הָעֹבֵר עַל־הַפְּקֻדִים מַחֲצִית הַשֶּׁקֶל בְּשֶׁקֶל הַקֹּדֶשׁ עֶשְׂרִים גֵּרָה הַשֶּׁקֶל מַחֲצִית הַשֶּׁקֶל תְּרוּמָה לַה׳
“This they shall give, every one that passes among them that are numbered, half a shekel after the shekel of the sanctuary: (a shekel is twenty gera:) a half shekel shall be the offering of the Lord.”
The Rambam’s words
To give a half-shekel each year, as [Exodus 30:13] states: "This shall be given by all those included in the census...."
ליתן מחצית השקל בכל שנה ושנה, שנאמר: "זה ייתנו, כל העובר על הפקודים" (שמות ל,יג).
Why · Sefer HaChinuch #105
Giving of the half shekel during the year
“It is from the roots of the commandment that the Holy One, blessed be He, wanted for the good of all of Israel and for their merit, that the hand of all be equal in the matter of the sacrifices that are brought in front of Him regularly the whole year, and in these matters that were mentioned.”
Who & when
“And [it] is practiced at the time of the [Temple], such that all of Israel is obligated to give it — whether those that are standing in the Land or those outside of the Land.”
Where in the Mishneh Torah
Hilchot Sheqel Dues הלכות שקלים