How do you say "I don't understand" in Japanese?

Quick use

Use わかりません (wakarimasen) when you need to say clearly that you do not understand.

It is safer than pretending you understood, especially with forms, instructions, payments, medicine, or directions.

Chunk or pattern

• This is a fixed phrase.
• Learn the whole line first.
• You can follow it with もういちどおねがいします if you need repetition.

Light form contrast

• わかります (wakarimasu): I understand.
• わかりません (wakarimasen): I do not understand.

Practical note

This phrase is direct but not rude. If you want to soften it, すみません、わかりません is a good version.