うちに details
write + while the chance lasts
kaku uchi ni
while the chance lasts; before the situation changes
meaning: while still writing
日本にいるうちに、一度は富士山に登ってみたい。
nihon ni iru uchi ni, ichido wa fujisan ni nobotte mitai.
I want to climb Mt. Fuji at least once while still living in Japan. neutral
冷めないうちに食べてね。
samenai uchi ni tabete ne.
Eat it before it gets cold. casual
Examples
while the situation still holds — act now, because the window will close
日本にいるうちに、一度は富士山に登ってみたい。
nihon ni iruuchini, ichido wa fujisan ni nobotte mitai.
I want to climb Mt. Fuji at least once while still living in Japan. neutral
覚えてるうちに書いとこ。
oboeteru uchi ni kaitoko.
Better jot it down while I still remember. casual
ないうちに — before the (usually unwanted) change happens; the signature negative use
冷めないうちに食べてね。
samenai uchi ni tabete ne.
Eat it before it gets cold. casual
暗くならないうちに帰りましょう。
kuraku naranai uchi ni kaerimashou.
Let's head home before it gets dark. neutral
お忘れにならないうちに、こちらにご記入ください。
o wasure ni naranai uchi ni, kochira ni go kinyuu kudasai.
Please fill this in before it slips your mind. formal
Formation
{V}うちにattaches to dictionary form{V-nai}うちにattaches to ない-form{N}のうちにattaches to noun
Notes
Related patterns
Similar
Both put the main event first in time, but まえに states the schedule off the dictionary form only, while ないうちに frames the same beforeness as beating a closing window — 暗くなるまえに帰る plans, 暗くならないうちに帰る races, and only うちに accepts the negative.
あいだに names a neutral interval with knowable endpoints (留守のあいだに), while うちに adds that the window is closing and the chance lapses with it — which is why deadlines and ない-clauses pull うちに.