Choosing až, když, or jestli

English uses when and if loosely, and lets a single when cover both "every time it rains" and "the moment you arrive (in the future)." Czech draws sharper lines. It has a separate conjunction for future "when" (až), a different one for habitual or past "when" (když), and yet another for "if/whether" (jestli / pokud / zda). The hardest leap for English speakers is the future-when split: "When you arrive, call me" is a future event, and Czech insists on až, not když. Get that one reflex right and most of the confusion disappears.

The quick answer

• až — "when" pointing at a future moment. Až přijdeš, zavolej. (When you arrive, call.)
• když — "when / whenever" for habitual, general, or past situations. Když prší, zůstávám doma. (When it rains, I stay home.) Colloquially also "if."
• jestli / pokud / zda — "if / whether" for a condition or an embedded yes/no question. Jestli prší, vezmi deštník. (If it's raining, take an umbrella.)

když — habitual, general, and past "when"

Když is the default "when" for everything that isn't a single future event. It covers:

• habitual / whenever: a repeated, general situation (present tense).
• past "when": a one-off or background event in the past.

The first sentence is a general truth (whenever it rains); the second is past; the third is habitual. None of them points at a single moment in the future, so all of them take když.

Colloquially, když also creeps into the "if" slot — když nechceš, nemusíš (if you don't want to, you don't have to). This is everyday-conversation usage; in writing, jestli/pokud is cleaner. We return to it under the if heading.

až — future "when"

Až marks a "when" that lies in the future and is presented as a point the main clause waits for: when X happens, then Y. This is precisely where English keeps when and a present-tense verb ("when you arrive…"), and where learners wrongly reach for když.

A defining feature: the až-clause normally uses the perfective present, which carries future meaning. Až přijdeš literally has a present-tense verb but means "when you will have arrived."

Compare the same scene as a habit versus a future event:

The first is what I do every day; the second is a plan for later today. English uses when for both; Czech splits them with když vs až. The fuller treatment of the temporal conjunctions, including jakmile ("as soon as"), lives on the temporal conjunctions page.

jestli / pokud / zda — "if / whether"

When the subordinate clause states a condition (if this, then that) or is an embedded yes/no question (I don't know whether…), Czech uses jestli, pokud, or zda. These are the "if/whether" conjunctions, and they are not interchangeable with když in careful Czech.

jestli — the everyday "if/whether," common in speech and neutral writing:

pokud — "if / provided that," a touch more formal, common in conditions (less so in embedded questions):

zda (and zdali) — (formal) "whether," for indirect questions in writing and careful speech:

For the difference between conditional if and whether in indirect questions, see the jestli / zda / -li page and indirect questions.

The když/jestli overlap

In casual speech, když and jestli both appear in the "if" slot, and natives mix them freely. But there is a meaning nuance worth knowing: jestli/pokud present the condition as genuinely open ("if — and maybe not"), while když leans toward "given that / since," treating the condition as more taken-for-granted.

In writing and exams, keep conditions in jestli/pokud and reserve když for "when."

The flowchart

1. Does the when-clause point at a single future moment the main clause waits for? → až (with the perfective present): Až přijdeš, zavolej.
2. Is it a habit, a general truth, or a past event — "whenever / when (back then)"? → když: Když prší… / Když jsem byl malý…
3. Is it a condition ("if") or an embedded yes/no question ("whether")? → jestli / pokud (condition) or jestli / zda (embedded question): Jestli prší… / Nevím, jestli…

Common mistakes

Using když for a future "when" — the signature English-transfer error:

Using až for a habit or general truth:

Using když for an open condition where careful Czech wants jestli:

Putting a future-tense verb in the až-clause instead of the perfective present:

Key takeaways

• až = future "when," with the perfective present: Až budu mít čas… / Až přijdeš…
• když = habitual / general / past "when," and colloquially "since/if": Když prší… / Když jsem byl malý…
• jestli / pokud / zda = "if / whether," for conditions and embedded yes/no questions: Jestli přijde… / Nevím, jestli…
• The trap is future "when": English keeps when, Czech switches to až.
• In writing, keep conditions out of když — use jestli/pokud.