shita-toki-vs-shita-totan

2021年1月8日2026年4月21日

Both した時 (shita toki) and したとたん (shita totan) can be translated as “when I did” — but they are not the same. した時 describes two events happening around the same point in time. したとたん expresses that the moment one action ended, something happened instantly and immediately after — often unexpectedly. This guide clarifies the difference with examples so you can use both patterns naturally.

Yuka

Quick question, Rei — when should I use した時 versus したとたん?

Rei

Ah, a classic mix-up! They’re related but definitely not interchangeable. I’ll explain with examples and it’ll make perfect sense.

TOC

At a Glance: した時 vs. したとたん

Feature	した時 (shita toki)	したとたん (shita totan)
Core meaning	When I did / At the moment of doing	The instant I did / The very moment
Timing	Simultaneous or around the same time	Immediately after — no gap at all
Unexpected nuance?	No	Often yes — sudden result
Can describe past habits?	Yes (子供の時)	No
Register	Casual to formal	Casual to formal
JLPT level	N4	N3

した時 (shita toki) — “When I Did / At the Time”

した時 is built from verb (past form) + 時 (toki, meaning “time” or “moment”). It describes a situation or state that existed at the same time as another event — a background snapshot. The two events can overlap in time rather than one causing the other.

Formation note: plain past form (た-form) + 時. The verb before 時 is always in the past tense (した, 食べた, 見た, etc.) when referring to a completed action at that time.

Example 1 — two things at the same time:

家に帰った時、お母さんはテレビを見ていた。
Ie ni kaetta toki, okaasan wa terebi wo mite ita.
When I got home, my mom was watching TV.

Example 2 — recalling a past state:

学生だった時、毎日勉強していた。
Gakusei datta toki, mainichi benkyou shite ita.
When I was a student, I studied every day.

Example 3 — a moment in the past:

東京に来た時、空気が違うと感じた。
Toukyou ni kita toki, kuuki ga chigau to kanjita.
When I came to Tokyo, I felt the air was different.

Yuka

Oh interesting! So した時 can mean that too? I only knew the basic meaning.

Rei

Yes! した時 is more versatile than most learners realize. Native speakers use it in all sorts of situations — not just the obvious ones.

したとたん (shita totan) — “The Instant / The Very Moment”

したとたん (also written した途端) uses 途端 (totan), which means “the very instant” or “just as.” This pattern emphasizes that the second event happened with zero delay after the first — it was immediate. There is also usually a sense of surprise or unexpectedness: the result was not planned or predicted.

Formation note: verb (past form, た-form) + とたん (or 途端 in kanji). The result that follows is usually something sudden or beyond the speaker’s control.

Example 1 — instant result:

外に出たとたん、雨が降り始めた。
Soto ni detara totan, ame ga furi hajimeta.
The instant I stepped outside, it started to rain.

Example 2 — unexpected physical reaction:

立ち上がったとたん、頭がくらくらした。
Tachiagatta totan, atama ga kurakura shita.
The moment I stood up, I felt dizzy.

Example 3 — sudden event:

ドアを開けたとたん、猫が飛び出してきた。
Doa wo aketa totan, neko ga tobidashite kita.
The instant I opened the door, the cat jumped out.

Yuka

What about したとたん? Is it used as often as した時 in daily conversation?

Rei

したとたん is super common too! The two words actually complement each other really well once you understand both.

The Key Difference: Overlap vs. Instant Result

Sentence	Pattern	Nuance
家に帰った時、母がいた。	した時	When I got home, my mother was there. (she was already there)
家に帰ったとたん、母が怒り始めた。	したとたん	The instant I got home, my mother started getting angry. (immediately, unexpectedly)
外に出た時、寒かった。	した時	When I went outside, it was cold. (state at that time)
外に出たとたん、倒れた。	したとたん	The moment I went outside, I collapsed. (instant, dramatic)

Important Constraint of したとたん

したとたん cannot be used for planned or intended results. The event that follows must be something that happened on its own — it is not something you caused or controlled. Compare:

Correct: 立ったとたん、転んだ。(The moment I stood up, I fell.) — unintended result
Incorrect: 立ったとたん、歩いた。(× The moment I stood up, I walked.) — you intended to walk

Decision Flowchart

You want to say "when I did X..."
        |
Did Y happen INSTANTLY and UNEXPECTEDLY the very second X ended?
(no gap; dramatic; often surprising)
        |
   YES                        NO — Y was just happening around the same time
    |                          or Y describes a background state
 したとたん (shita totan)       した時 (shita toki)
"The instant I did X, Y       "When I did X, Y was happening"
 happened immediately"         (simultaneous, neutral)