also: づつ
Attaches to a quantity or number to indicate an equal distribution per person, item, or unit.
I gave two cookies to each person.
at a time; in portions
Indicates doing something in repeated small amounts or stages, often with a sense of gradual progression.
My Japanese is getting better little by little.
I handed out the apples three at a time.
These notebooks are 100 yen each.
I make it a rule to read three pages at a time every day.
My Japanese has been improving little by little.
Please call out the names one at a time.
I'm reading five pages of the book each day, bit by bit.
ごとに means 'every' or 'at each interval' and highlights repetition across units, while ずつ highlights an equal amount given to or done by each unit.
Standard kana spelling; the kanji 宛 is rarely used.
Alternate kana spelling, historically used but now less common than ずつ.
Rare kanji form; learners should use kana.
Modern ずつ is the standard spelling of earlier づつ, a distributive particle already found in classical Japanese; its deeper origin is uncertain.