打小九九

dǎxiǎojiǔjiǔ ㄉㄚˇ ㄒㄧㄠˇ ㄐㄧㄡˇ ㄐㄧㄡˇ

    • to calculate quietly for one's own advantage

Character by character

Saying俗语俗語

Idiom惯用语 · Widely known

Literally
work out the little nine-nines
Meaning
A variant of 打小算盘: to calculate quietly for your own advantage. Mocking.

Sources