いいじゃん

that's good / why not

→ 良い

phrase Uncommon #18,704

that's good / why not Informal expression combining いい (good) with じゃん, a casual form of じゃない. It can express approval, reassurance, or encouragement, often with the sense of “isn't that fine?” or “you might as well.”

JA: 疲れてるなら、今日は休めばいいじゃん。

EN: If you're tired, you might as well rest today.

（信代）いいじゃん

(Nobuyo) Sounds good.

— 万引き家族 (2018)

（将也）いいじゃんいいじゃん

(Shoya) That’s great, that’s great.

— 映画聲の形 (2016)

別にいいじゃんかよ。

It's not like there's anything wrong with it.

お前のネクタイ、いいじゃん。

I like your tie.

泣きたいなら思いっきり泣けばいいじゃん。

If you want to cry, then just cry your heart out.

お前の成績は俺よりいいじゃん。

Your grades are better than mine.

（信代）ねえ亜紀もさちょっとは入れたらいいじゃん

(Nobuyo) Hey, Aki, you should chip in a little too.

— 万引き家族 (2018)

眠いなら寝ればいいじゃん。

If you're sleepy, why don't you just go to sleep?

いいじゃん

That’s great!

— グッバイ、レーニン！ (2003)