Temporal Conjunctions: když, až, jakmile | Czech Grammar

English gets by with one word, when, for an enormous range of time clauses: "when I was little," "when I get home," "when it rains." Czech splits that single when across several conjunctions, and choosing the wrong one is one of the most persistent learner errors — not because the rules are subtle, but because English never trained you to make the distinction. The headline rule, the one that catches everyone: use když for the past and present, but až for the future. This page sorts out the whole cluster.

když — when / whenever (present and past)

když is your default "when" for anything that is not in the future: a single past event, a past habit, a present habit, or a general "whenever."

Když jsem byl malý, bydleli jsme na vesnici.

When I was little, we lived in a village. (single past situation)

Když prší, zůstávám doma.

When(ever) it rains, I stay home. (present general truth)

Vždycky se zasměju, když si na to vzpomenu.

I always laugh when I remember it. (present habit)

Když jsem ho viděl naposledy, vypadal unaveně.

When I last saw him, he looked tired. (one past event)

So když covers two English "whens" at once: the specific "when X happened" and the habitual "whenever X happens." What it does not do is reach into the future — that job belongs to až.

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když = the "when" of memory and habit. If the clause is about the past or about what generally happens, it's když.

až — when (future only)

For a time clause pointing at the future, Czech requires až, never když. "When I get home, I'll call you" describes a future moment, so it must be až. The verb inside the až clause is itself future — a perfective present (přijdu) or a budu future (budu mít).

Až přijdu domů, zavolám ti.

When I get home, I'll call you.

Až budu mít čas, pomůžu ti s tím.

When I have time, I'll help you with it.

Až dostuduješ, co budeš dělat?

When you finish your studies, what will you do?

Zavoláme ti, až přiletíme.

We'll call you when we land.

This is the single biggest trap, so it's worth stating plainly: English uses the present tense in its "when" clause for future meaning ("when I get home…"), which makes the future invisible. Czech makes the future explicit and demands až. There is no version of this where když přijdu domů means "when I get home" — když simply cannot express a future when.

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The English present-for-future ("when I get there") is the trap. The clause is about the future, so Czech uses až + a future verb: až přijdu. Never *když přijdu for "when I arrive."

For how the verb inside these clauses is built, see choosing the right future.

jakmile — as soon as

jakmile sharpens "when" into "as soon as" — the instant one thing happens, the next follows. It works for both past and future, and in the future it patterns with až (future verb inside).

Jakmile to dočtu, půjčím ti tu knihu.

As soon as I finish reading it, I'll lend you the book.

Jakmile zazvonil budík, vyskočil z postele.

As soon as the alarm rang, he jumped out of bed. (past)

Dej mi vědět, jakmile dorazíš.

Let me know as soon as you arrive.

Use jakmile when you want to stress immediacy; use až when you just mean "at the future time that." Often either works, but jakmile adds the "the moment that" punch.

než — before

než introduces a "before" clause. Note that it is the same word used in comparisons ("bigger than"); here it is temporal. The clause names the later event, and the než event happens first.

Než odejdeš, zhasni prosím světlo.

Before you leave, please turn off the light.

Stihl jsem to dočíst, než přijela.

I managed to finish reading it before she arrived.

Než se naděješ, bude léto.

Before you know it, it'll be summer.

For the comparison-versus-time split of než, see než for comparison and time.

dokud — as long as / until (with a twist)

dokud has two faces. With an affirmative verb it means "as long as" / "while" — for the duration that something holds. With a negated verb it means "until" — and this is the surprise: where English says "until I finish," Czech says dokud neskončím, literally "as long as I don't finish." The negation is obligatory and is not a real negation in meaning.

Dokud máš čas, odpočívej.

As long as you have time, rest. (affirmative dokud = 'as long as')

Počkej, dokud nepřijdu.

Wait until I come. (literally 'as long as I don't come')

Nikam nechoď, dokud to nedoděláš.

Don't go anywhere until you finish it.

Dokud neuvidím důkaz, nevěřím tomu.

Until I see proof, I don't believe it.

This obligatory "empty" negation feels deeply wrong to English speakers, who hear a double negative. But in Czech dokud ne- is simply the way to say "until." The mental translation is: "until X" → "dokud X-NOT." (This is a cousin of the broader rule that certain words force a negated verb — see negative concord.)

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"Until" = dokud … ne- with a negated verb, always. Počkám, dokud nepřijdeš = "I'll wait until you come." Drop the ne- and you change the meaning to "as long as you (don't) come."

zatímco — while (two things at once)

zatímco means "while" in the sense of two things happening simultaneously — and often with a flavour of contrast, "whereas." Both verbs are typically imperfective (ongoing).

Zatímco jsem vařil, ona prostírala stůl.

While I was cooking, she was setting the table.

Zatímco jedni protestovali, druzí klidně pracovali.

While some were protesting, others calmly kept working. (contrastive 'whereas')

Don't use zatímco for "as soon as" or for a point in time — it is specifically about overlapping stretches.

Quick decision guide

You mean…	Use	Example
when (past event / habit / general)	když	Když jsem byl malý…
when (future)	až	Až přijdeš, zavoláme.
as soon as	jakmile	Jakmile skončím…
before	než	Než odejdeš…
as long as / while (duration)	dokud (+ affirmative)	Dokud máš sílu…
until	dokud (+ negated verb)	Počkej, dokud nepřijdu.
while (two things at once / whereas)	zatímco	Zatímco vařím, ty ukliď.

How English differs

English collapses "when (past)" and "when (future)" into one word and even uses the present tense for future time clauses ("when I get there"). Czech refuses both shortcuts: it has separate conjunctions (když vs až) and puts a genuinely future verb in the future clause. English "until" is a single clean preposition/conjunction; Czech expresses it with dokud + a negated verb, which has no English parallel and reliably trips learners. Finally, English "while" does double duty (time + contrast); Czech mostly hands the time-overlap-plus-contrast sense to zatímco.

Common Mistakes

❌ Když přijdu domů, zavolám ti.

Incorrect — this is a future 'when', so it must be až.

✅ Až přijdu domů, zavolám ti.

When I get home, I'll call you.

❌ Až jsem byl malý, hrál jsem fotbal.

Incorrect — a past 'when' takes když, not až.

✅ Když jsem byl malý, hrál jsem fotbal.

When I was little, I played football.

❌ Počkej, dokud přijdu.

Incorrect — 'until' requires the negated verb: dokud nepřijdu.

✅ Počkej, dokud nepřijdu.

Wait until I come.

❌ Až bude pršet, byl jsem doma.

Incorrect — mismatched time frames; a future až clause can't pair with a past main clause here.

✅ Když pršelo, byl jsem doma.

When it rained, I was at home.

❌ Zavolej mi, zatímco dorazíš.

Incorrect — 'as soon as you arrive' is a point in time, not an overlap; use jakmile.

✅ Zavolej mi, jakmile dorazíš.

Call me as soon as you arrive.

Key Takeaways

když = "when" for the past, present, and habits (Když jsem byl malý…, Když prší…).
až = "when" for the future — never když (Až přijdeš, zavoláme).
jakmile = "as soon as"; než = "before"; zatímco = "while / whereas."
dokud
- affirmative = "as long as"; dokud
  - negated verb = "until" (Počkej, dokud nepřijdu).
The two killer traps: using když for a future "when," and forgetting the obligatory ne- after dokud for "until."

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