てしまう for Completion and Regret in Japanese

In Brief

Attach しまう to a verb’s て-form to present an action as fully completed or its result as final: 食べてしまった means “ate it all” or “ended up eating it.” Depending on the situation and tone, the same pattern can suggest accident, disappointment, embarrassment, or regret. In casual speech, てしまう becomes ちゃう, while でしまう becomes じゃう.

Overview

てしまう combines a main verb in the て-form with しまう. The て-form is a connecting form of a verb; if you can already make forms such as 食べて, 書いて, and 読んで, you have the foundation for this pattern. In this construction, しまう behaves as an auxiliary verb (a helping verb that adds meaning to the main action).

The pattern has two closely related uses. It can emphasize completion: the action is done fully, all the way to its endpoint. It can also highlight an unwanted or unplanned result: something happened, and the speaker now reacts to the outcome. These are not two rigid dictionary meanings. The idea of crossing an endpoint often makes a result feel irreversible, which allows regret, surprise, or annoyance to arise from context.

English has no single matching form. Depending on the sentence, natural translations include “finish,” “completely,” “all up,” “accidentally,” “unfortunately,” or “end up.” Sometimes English needs no extra word at all: 忘れてしまった！ can simply be “I forgot!” said with dismay. At B2, the main skill is therefore interpreting the speaker’s attitude rather than replacing every てしまう with one fixed English phrase.

How It Works

Build the full form

Start with the て-form and add しまう. This works after both て and で.

Dictionary form	て-form	Pattern	Typical interpretation
食べる	食べて	食べてしまう	eat completely; end up eating
忘れる	忘れて	忘れてしまう	forget, regrettably
書く	書いて	書いてしまう	finish writing; accidentally write
読む	読んで	読んでしまう	read completely; end up reading
壊す	壊して	壊してしまう	break, unfortunately

The main verb stays in the て-form. Tense, politeness, and negation are marked on しまう:

Function	Form	Example	Possible meaning
Plain non-past	てしまう	食べてしまう	will eat it all / will end up eating
Polite non-past	てしまいます	食べてしまいます	eat or will eat it all
Plain past	てしまった	食べてしまった	ate it all / accidentally ate it
Polite past	てしまいました	食べてしまいました	ate it all, with a polite style
Plain negative	てしまわない	食べてしまわない	will not finish or end up eating
Polite negative	てしまいません	食べてしまいません	polite negative
Volitional	てしまおう	食べてしまおう	let’s/I’ll get it eaten
Polite volitional	てしまいましょう	食べてしまいましょう	let’s finish eating it

Past forms are especially common when a speaker reacts to an outcome that has already occurred. The pattern itself does not tell you whether the action was intentional; the verb, situation, adverbs, and tone do that work.

Completion: reaching the endpoint

With a bounded action—one that has an obvious endpoint—てしまう can mean that the action is completely finished:

• 本を一晩で読んでしまった。 — “I read the book in one night.”
• 宿題を先にやってしまおう。 — “I’ll get the homework finished first.”

This use need not be negative. The speaker may feel satisfaction, relief, determination, or simply emphasize that nothing remains. Words such as 全部 “all” and 最後まで “to the end” strongly support this reading.

Unwanted outcome, accident, or regret

When the event is undesirable, てしまう draws attention to the unfortunate completed result:

• 鍵をなくしてしまいました。 — “Unfortunately, I lost my key.”
• 電車で寝てしまった。 — “I accidentally fell asleep on the train.”

Do not assume that てしまう literally means “by accident.” A person may have acted deliberately and regretted it afterward: 言ってしまった could mean “I said it—and now I wish I hadn’t.” Conversely, an unintended event may be presented neutrally without てしまう.

Casual contractions

In relaxed conversation, the full sequence contracts according to the end of the て-form:

Full sequence	Casual contraction	Non-past example	Past example
〜てしまう	〜ちゃう	食べちゃう	食べちゃった
〜でしまう	〜じゃう	飲んじゃう	飲んじゃった

The choice between ちゃう and じゃう is not based directly on the dictionary ending. First make the correct て-form: 読む → 読んで → 読んじゃう, but 書く → 書いて → 書いちゃう.

The contracted ending changes like the verb しまう:

Meaning	〜て full form	〜て casual	〜で full form	〜で casual
non-past	食べてしまう	食べちゃう	飲んでしまう	飲んじゃう
past	食べてしまった	食べちゃった	飲んでしまった	飲んじゃった
negative	食べてしまわない	食べちゃわない	飲んでしまわない	飲んじゃわない
volitional	食べてしまおう	食べちゃおう	飲んでしまおう	飲んじゃおう

Examples in Context

The translation changes with the likely attitude and situation. The note identifies a natural reading, not a meaning mechanically encoded by the form.

Japanese	English	Note
全部食べてしまいました。	I ate it all.	Complete consumption; context may add regret.
忘れてしまった！	I forgot!	The exclamation suggests dismay.
電話番号を間違えちゃった。	I got the phone number wrong.	Casual; an unintended mistake.
最後まで読んでしまいましょう。	Let’s read it through to the end.	Deliberate completion, not regret.
レポートはもう書いてしまいました。	I’ve already finished writing the report.	Completion, possibly sooner than expected.
ケーキを一人で全部食べちゃった。	I ate the whole cake by myself.	Casual; may convey guilt or surprise.
大事な写真を消してしまいました。	I accidentally deleted an important photo.	The bad result makes the accidental reading natural.
ソファで寝ちゃった。	I fell asleep on the sofa.	Informal speech; likely unplanned.
面白くて、朝まで見てしまった。	It was so interesting that I ended up watching until morning.	The action continued farther than intended.
彼に秘密を話してしまった。	I told him the secret—and I regret it.	The telling may have been deliberate; regret concerns the result.
この仕事、今日中にやってしまおう。	Let’s get this job done today.	Determination and completion.
財布を電車に置いてきてしまった。	I left my wallet on the train.	An unfortunate result with another て-form pattern inside it.
そんなことを言うと、彼女が怒っちゃうよ。	If you say that, she’ll get angry.	Casual warning about an undesirable future result.

Common Mistakes

Treating it as a literal word for “accidentally”

• Misleading: 宿題をしてしまった = “I accidentally did my homework.”
• Better reading without special context: 宿題をしてしまった = “I finished the homework / got it done.”
• Why: Homework has a natural endpoint, so completion is the obvious reading. An accidental interpretation needs a situation that supports it.

Using ちゃう after a で-form

• Wrong: 読んちゃった。
• Right: 読んじゃった。
• Why: 読む becomes 読んで, so でしまった contracts to じゃった. With a て-form such as 食べて, use 食べちゃった.

Conjugating the main verb twice

• Wrong: 食べたしまった。
• Right: 食べてしまった。
• Why: Put the main verb in the て-form. Past tense is carried by しまった, not by 食べる.

Assuming every completed action takes てしまう

• Unnatural as a neutral report: 昨日、仕事をしてしまいました。 when you only mean “I worked yesterday.”
• Neutral: 昨日、仕事をしました。
• Completion-focused: 昨日、仕事を全部してしまいました。 — “I finished all the work yesterday.”
• Why: てしまう adds a viewpoint on the endpoint or result. Ordinary past events do not require it.

Using a casual contraction in formal communication

• Too casual in a formal apology: 資料を消しちゃいました。
• Appropriate: 資料を消してしまいました。 — “I’m afraid I deleted the document.”
• Why: ちゃう/じゃう belongs mainly to relaxed speech. The full form fits workplace explanations, formal apologies, and careful writing.

Usage Notes

The speaker’s attitude comes from context

A single sentence can permit more than one reading. 全部食べてしまった may be a proud report that someone finished a difficult meal, a guilty confession that nothing was left for others, or surprise at how much they ate. English speakers often look for a word corresponding to “accidentally,” but Japanese listeners use context, facial expression, intonation, and words such as うっかり “carelessly/by mistake” to narrow the meaning.

If the distinction matters, make it explicit:

• うっかり消してしまった。 — “I carelessly deleted it.”
• わざと消した。 — “I deleted it on purpose.”
• やっと全部読んでしまった。 — Depending on tone, “I finally read it all,” though 読み終えた may be clearer for neutral accomplishment.

Full and contracted forms

てしまいます/てしまいました are normal in polite conversation. Plain てしまう/てしまった suits informal but uncontracted speech and much writing. ちゃう/じゃう are highly frequent among friends and family and in dialogue, but they can sound overly relaxed in a report, essay, customer interaction, or formal apology.

Contractions do not automatically make the emotion stronger. They primarily mark conversational style. Tone can make 忘れちゃった sound embarrassed, playful, irritated, or genuinely upset.

Written spacing and lexical しまう

Japanese is normally written without spaces: 食べてしまう. In learning materials, the elements may be visually separated for explanation.

Also distinguish this grammar pattern from lexical しまう, “put away/store”:

• 服をたんすにしまう。 — “Put the clothes in the dresser.”
• 服を捨ててしまう。 — “Throw the clothes away completely / unfortunately throw them away.”

The first しまう is the main action. In the second, it follows a て-form and adds completion or an attitude toward the result.

Beyond the Basics: Perspective and Contrast

Finality without personal regret

The regrettable event does not have to affect the speaker, and the grammatical subject does not have to be a person. 花が枯れてしまった means “The flowers have withered,” with sadness or concern about the resulting state. This shows why “regret” is only a convenient label: the broader effect is that the speaker presents the completed outcome as noteworthy, often unfortunate.

In questions or statements about another person, avoid automatically attributing regret to that person. 田中さんは帰ってしまった can mean “Mr. Tanaka has gone home,” with the speaker disappointed that he left. The action may have been perfectly intentional from Mr. Tanaka’s point of view.

てしまう versus plain past and completion verbs

Form	Main focus	Example	Natural interpretation
plain past	event as a fact	本を読んだ	I read the book.
てしまった	completed/final result, often with attitude	本を読んでしまった	I read it all / ended up reading it.
〜終わった	explicit end of an activity	本を読み終わった	I finished reading the book.
〜切った	doing something fully or to the limit	本を読み切った	I read the whole book through.

These forms overlap, but they are not interchangeable. 読み終わる neutrally names the end of reading. 読み切る emphasizes carrying the action through. 読んでしまう presents the resulting completion through the speaker’s perspective and can invite an emotional reading.

Scope in longer sentences

The material immediately before しまう forms one unit with it. That unit can then take particles or connect to further grammar:

• 食べてしまったので、もうありません。 — “Because I ate it all, there is none left.”
• 忘れてしまわないように、メモします。 — “I’ll make a note so that I don’t forget.”
• 言ってしまったことは取り消せない。 — “What has been said cannot be taken back.”

Notice that negative てしまわない often means preventing an unwanted outcome. It does not simply negate regret; it negates the completed event itself.

Practice Tips

1. Classify by context, not translation. For each example you meet, label it “completion,” “unwanted result,” or “both.” Then identify the clue: 全部, the type of event, an apology, or the surrounding story.
2. Transform full and casual forms aloud. Practice pairs such as 忘れてしまった → 忘れちゃった and 飲んでしまった → 飲んじゃった. Always derive the contraction from the て-form.
3. Create contrasting mini-situations. Use one sentence such as ケーキを食べてしまった in two contexts: finishing it deliberately and eating it despite a diet. This trains the contextual nuance that a word-for-word English gloss cannot show.

Related Concepts

• Prerequisite: て-Form — supplies the connecting verb form used before しまう.