also: づつ
suffix
Attaches to a quantity or number to indicate an equal distribution per person, item, or unit.
一人に二つずつクッキーをあげた。
I gave two cookies to each person.
このノートは一冊百円ずつです。
These notebooks are 100 yen each.
suffix
at a time; in portions
Indicates doing something in repeated small amounts or stages, often with a sense of gradual progression.
少しずつ日本語が上手になっている。
My Japanese is getting better little by little.
毎日三ページずつ読むことにしている。
I make it a rule to read three pages at a time every day.
Rare kanji form; learners should use kana.
ごとに means 'every' or 'each time' and emphasizes repetition or intervals, while ずつ focuses on equal distribution or gradual accumulation.
Derived from the classical Japanese particle つつ, which indicated repetition or continuation. The exact historical development is uncertain, but ずつ is now a standard suffix for distribution.