Hindi separates two questions that English sometimes blurs with when: कब asks for a point or occasion in time, while कितनी देर asks for a length of time. Both normally stay in the part of the clause where the answer would appear. Hindi does not move them obligatorily to the front or invert the subject and auxiliary as English does.
कब asks for a time or occasion
Use कब when the expected answer is a clock time, date, day, stage, or occasion. It is invariable: it does not agree with the subject and does not change for tense.
तुम कब लौटोगे?
tum kab lauṭoge?
When will you return? (familiar)
आपकी नई कक्षा कब शुरू होगी?
āpkī naī kakṣā kab śurū hogī?
When will your new class begin? (honorific)
दुकान रविवार को कब खुलती है?
dukān ravivār ko kab khultī hai?
When does the shop open on Sundays?
The neutral position is usually immediately before the element being questioned or before the predicate: तुम कब लौटोगे? A fronted कब is possible when the time itself is strongly contrasted—कब लौटोगे तुम?—but it sounds more insistent or emotionally marked. English fronting is grammatical machinery; Hindi fronting is discourse choice.
If a precise clock time is expected, कितने बजे “at what time” is more specific than कब:
फ़िल्म कितने बजे ख़त्म होगी?
film kitne baje xatm hogī?
What time will the film end?
कितनी देर asks for duration
देर is a feminine noun, so the interrogative quantifier agrees with it: कितनी देर, literally “how much time.” It asks how long an activity or state lasts, not when it occurs.
तुम यहाँ कितनी देर रुकोगे?
tum yahā̃ kitnī der rukoge?
How long will you stay here? (familiar)
बैठक कितनी देर चली?
baiṭhak kitnī der calī?
How long did the meeting last?
आपको वहाँ पहुँचने में कितनी देर लगेगी?
āpko vahā̃ pahũcne meṃ kitnī der lagegī?
How long will it take you to get there? (honorific)
The common construction X को Y करने में कितनी देर लगेगी? presents the experiencer with को, puts the activity in -ने में, and makes देर the subject of लगना. English instead makes it a dummy subject: “How long will it take?” Do not imitate that English syntax in Hindi.
कितना समय is a more formal alternative, common in notices, interviews, and planning. Everyday conversation strongly favors कितनी देर.
इस प्रक्रिया में कितना समय लगेगा?
is prakriyā meṃ kitnā samay lagegā?
How much time will this process take? (formal)
The masculine समय requires कितना, whereas feminine देर requires कितनी. The meaning is similar; agreement follows the Hindi noun, not English how long.
Starting points and endpoints: कब से and कब तक
Postpositions refine the temporal question. कब से asks “since when / starting when,” and कब तक asks “until when / by when.” Unlike the person interrogative कौन, कब does not develop an oblique stem before these postpositions.
तुम इस मोहल्ले में कब से रह रहे हो?
tum is mohalle meṃ kab se rah rahe ho?
Since when have you been living in this neighborhood?
यह रास्ता कब तक बंद रहेगा?
yah rāstā kab tak band rahegā?
Until when will this road remain closed?
आवेदन कब तक भेजना है?
āvedan kab tak bhejnā hai?
By when does the application have to be sent?
With an ongoing activity, कितनी देर से asks for the amount of elapsed time, while कब से asks for its starting point. The answers reveal the contrast: सुबह से answers कब से?; दो घंटे से answers कितनी देर से?
तुम कितनी देर से मेरा इंतज़ार कर रहे हो?
tum kitnī der se merā intazār kar rahe ho?
How long have you been waiting for me?
आप कब से बाहर इंतज़ार कर रहे हैं?
āp kab se bāhar intazār kar rahe haiṃ?
Since when have you been waiting outside? (honorific)
Similarly, कितनी देर तक asks the duration up to an endpoint: हम कितनी देर तक रुकें? “How long should we stay?” See postpositions with interrogatives for the broader case pattern.
Information questions versus polar questions
Clause-initial क्या marks a yes–no question. कब and कितनी देर request missing information and normally do not need it.
क्या ट्रेन आज आएगी?
kyā ṭren āj āegī?
Will the train come today?
ट्रेन आज कब आएगी?
ṭren āj kab āegī?
When will the train come today?
In the first question, the answer can be हाँ or नहीं. In the second, the answer supplies a time. Learners sometimes produce क्या ट्रेन कब आएगी? as a direct copy of English question structure. In neutral Hindi that unnecessarily combines a polar marker with an information word. A sequence containing both can exist only when क्या itself means “what” or when special discourse creates two layers of questioning; it is not the default way to ask when.
Hindi information-question contours vary by dialect, focus, and stance; a neutral कब question may end low or falling as well as level or rising. A particularly sharp fall, together with context and stress, can contribute impatience, challenge, or a rhetorical reading, but falling pitch is not inherently marked.
Politeness, formality, and echo questions
कब and कितनी देर themselves do not change for politeness. Respect is carried by आप, plural/honorific agreement, and wording such as कृपया (formal).
तुम कब खाली हो? — शाम को।
tum kab khālī ho? — śām ko.
When are you free? — In the evening. (informal/familiar)
आप कब उपलब्ध होंगी? — सोमवार की सुबह।
āp kab upalabdh hoṅgī? — somvār kī subah.
When will you be available? — Monday morning. (formal/honorific, addressed to a woman)
An echo question repeats a surprising time with prominent stress. It is not a neutral request for entirely new information:
उड़ान कब है—सुबह चार बजे?
uṛān kab hai—subah cār baje?
The flight is when—at four in the morning?
In fast conversation, simply कब? or कितनी देर? can serve as a complete clarification question (informal). The omitted clause is recovered from context.
Common Mistakes
Assuming only one neutral word order
कब होगी आपकी बैठक?
kab hogī āpkī baiṭhak?
When will your meeting be? (natural predicate-first question)
✅ आपकी बैठक कब होगी?
āpkī baiṭhak kab hogī?
When will your meeting be?
Both orders are idiomatic. The predicate-first form is common in questions and need not be treated as English-style inversion; discourse and prosody determine which ordering fits best.
Adding clause-initial क्या to a wh-question
❌ क्या तुम कब आओगे?
Incorrect as a neutral ‘When will you come?’—क्या asks yes or no while कब asks for a time.
✅ तुम कब आओगे?
tum kab āoge?
When will you come?
Asking for a duration with कब
❌ बैठक कब चली?
Incorrect for ‘How long did the meeting last?’—कब asks when it occurred.
✅ बैठक कितनी देर चली?
baiṭhak kitnī der calī?
How long did the meeting last?
Ignoring agreement with देर
❌ यहाँ कितना देर रुकना है?
Incorrect—feminine देर requires कितनी.
✅ यहाँ कितनी देर रुकना है?
yahā̃ kitnī der ruknā hai?
How long are we supposed to stay here?
Key Takeaways
Use कब for a time point and कितनी देर for a duration. Add से for a starting point and तक for an endpoint; distinguish कब से “since when” from कितनी देर से “for how long.” Keep the wh-expression in its natural focused position, preserve ordinary Hindi word order, and reserve clause-initial क्या for yes–no questions.
Related Topics
- Yes-no questions with clause-initial क्याA1 — Form neutral and biased yes–no questions with initial क्या while preserving ordinary Hindi word order, agreement, and interrogative intonation.
- Yes-no questions by intonation aloneA1 — Ask neutral, polite, and echo yes-no questions with ordinary Hindi word order and questioning intonation, without an overt question word.
- क्या as what versus question markerA1 — Distinguish argument क्या meaning ‘what’ from clause-initial क्या marking a yes-no question by position, answer type, and grammatical behavior.
- कहाँ किधर and कहाँ सेA2 — Distinguish कहाँ for location or destination, किधर for direction, and कहाँ से for source, origin, or starting point.
- Postpositions with interrogativesB1 — Build case-marked questions with किस, किन, कहाँ, कब, and compound postpositions without copying English preposition stranding.