てしまう (Completion/Regret) in Japanese

Overview

The grammar pattern てしまう (te shimau) is one of the most expressive and frequently used constructions in Japanese. It combines the て-form of a verb with しまう to convey two related but distinct meanings: completion of an action (often with a sense of finality) and regret or unintended consequences. Context determines which nuance applies.

At the B2 level, you already know the て-form well. Adding しまう gives you the ability to express emotional coloring that English often handles through tone of voice or adverbs like "accidentally," "unfortunately," or "completely." This is a pattern that native speakers use dozens of times a day, and mastering it will make your Japanese sound significantly more natural.

In casual speech, てしまう contracts to ちゃう (after て) and じゃう (after で), which are extremely common and worth learning alongside the full form.

How It Works

Formation

て-Form Ending	Full Form	Casual Contraction
~て	~てしまう	~ちゃう
~で	~でしまう	~じゃう

Conjugation of the Casual Forms

Form	ちゃう	じゃう
Dictionary	ちゃう	じゃう
Polite (ます)	ちゃいます	じゃいます
Past (た)	ちゃった	じゃった
Past polite	ちゃいました	じゃいました
て-form	ちゃって	じゃって
Negative	ちゃわない	じゃわない

Two Core Meanings

Meaning	Signal	Example
Completion	action done thoroughly, completely	全部食べてしまった (ate it all up)
Regret/Unintended	action happened unfortunately, accidentally	忘れてしまった (forgot — wish I hadn't)

How to Tell Which Meaning

Clue	Likely Meaning
Positive action, intentional context	completion
Negative outcome, mistake, accident	regret
全部, すっかり (completely) present	completion
つい (inadvertently), うっかり (carelessly) present	regret
Volitional (～しまいましょう)	completion
Past tense, negative emotion	regret

Examples in Context

Japanese	English	Note
全部食べてしまいました。	I ate it all.	Completion — thorough
忘れてしまった！	I forgot! (with regret)	Regret — unintended
電話番号を間違えちゃった。	I accidentally got the wrong phone number.	Casual, regret
最後まで読んでしまいましょう。	Let's read it to the end.	Completion — volitional
財布を家に忘れてきちゃった。	I left my wallet at home.	Casual, regret
この本、一日で読んでしまった。	I read this whole book in one day.	Completion — impressive
つい食べ過ぎてしまいました。	I inadvertently ate too much.	Regret with つい
雨が降ってきてしまった。	It started raining (unfortunately).	Regret — unwelcome event
宿題を全部やってしまおう。	Let's get all the homework done.	Completion — determination
うっかり寝てしまって、遅刻した。	I carelessly fell asleep and was late.	Regret with うっかり
壊れてしまったので、新しいのを買います。	It broke, so I'll buy a new one.	Regret — unfortunate result
さっさと片付けてしまいなさい。	Hurry up and get it cleaned up.	Completion — imperative

Common Mistakes

Using てしまう when there is no emotional coloring

• Wrong: 毎日ご飯を食べてしまいます。 (for a routine action)
• Right: 毎日ご飯を食べます。
• Why: てしまう adds emotional weight — completion or regret. For neutral daily actions, the plain form is correct. Adding しまう here implies you eat reluctantly or excessively.

Forgetting the casual contractions in conversation

• Wrong: 食べてしまった (in very casual speech with friends)
• Right: 食べちゃった
• Why: Using the full form てしまう in casual conversation sounds stiff. With close friends, ちゃう/じゃう is far more natural. Save the full form for polite or written contexts.

Mixing up ちゃう and じゃう

• Wrong: 飲んちゃった
• Right: 飲んじゃった
• Why: The contraction follows the て-form: if the て-form uses で (飲んで), the contraction is じゃう. If it uses て (食べて), the contraction is ちゃう.

Using てしまう with stative verbs incorrectly

• Wrong: 知ってしまっている (for simply knowing)
• Right: 知ってしまった (came to know — can't unknow it)
• Why: てしまう with stative verbs usually refers to the moment of change, not the ongoing state. 知ってしまった means "I found out (and wish I hadn't)" — a completed moment of discovery.

Usage Notes

In spoken Japanese, the casual contractions ちゃう and じゃう are overwhelmingly preferred over the full てしまう. You will hear them in virtually every casual conversation. The full form appears in polite speech (てしまいました), formal writing, and when emphasizing the emotional weight deliberately.

The regret nuance is often subtle. Sometimes てしまう simply adds a sense of "oh well" or mild surprise rather than deep regret. For instance, もう終わっちゃった (it's already over) might express mild disappointment rather than strong regret.

In business Japanese, てしまいまして is used as an apology softener: 遅れてしまいまして、申し訳ございません (I'm sorry for being late — the しまう acknowledges it was unfortunate).

The completion meaning is particularly common with volitional forms (しまおう, しまいましょう) when expressing determination to finish something.

Practice Tips

• For one week, keep a "regret diary" in Japanese. Write three things each day that happened unintentionally or that you wish hadn't happened, using てしまう. This builds the regret meaning into your muscle memory.

• Practice converting between full and casual forms rapidly: say a sentence with てしまう, then immediately repeat it with ちゃう/じゃう. Speed drills help make the casual forms automatic.

• Watch comedy anime or variety shows where characters react to mishaps. These are goldmines for てしまう/ちゃう usage, as characters constantly express surprise and regret at unexpected outcomes.

Related Concepts

• Prerequisite: て-Form — the foundational conjugation needed to build this pattern
• Next steps: ていく/てくる (direction) — another て-form compound expressing directional change
• Next steps: ておく (preparation) — て-form compound for advance preparation