How to Say I Don't Know in Spanish: 15 Natural Phrases

To say I don't know in Spanish, use No sé /no ˈse/. It is the everyday answer you can use almost anywhere. For a specific fact, say No lo sé /no lo ˈse/; for stronger emphasis, say No tengo idea /no ˈteŋɡo iˈðea/; and for a polite, careful answer, use No sabría decirte /no saˈβɾia ðeˈsiɾte/.

Spanish is spoken by more than 600 million potential speakers worldwide, according to the Instituto Cervantes, and it is an official language in 20 countries. That scale means the exact accent and favorite expression change by region, but No sé /no ˈse/ works everywhere from Madrid to Mexico City to Buenos Aires.

The key is choosing an answer that matches how certain you are, who you are speaking to, and whether the topic is serious. These phrases will help you sound honest without sounding abrupt.

If you are building basic conversation skills, pair these answers with the greetings in our guide to how to say hello in Spanish. Knowing how to begin a conversation and how to ask for clarification removes a lot of pressure from real interactions.

The essential phrase: No sé

No sé /no ˈse/ literally means I do not know. It comes from the verb saber /saˈβeɾ/, meaning to know information, facts, answers, or how to do something.

Use it on its own when the context is obvious:

• ¿Dónde está Ana? /ˈdonde esˈta ˈana/
  Where is Ana?

• No sé. /no ˈse/
  I don't know.

You can also put an indirect question after it:

• No sé dónde está. /no ˈse ˈdonde esˈta/
  I don't know where she is.

• No sé qué pasó. /no ˈse ke paˈso/
  I don't know what happened.

• No sé cómo hacerlo. /no ˈse ˈkomo aˈseɾlo/
  I don't know how to do it.

• No sé cuándo llega. /no ˈse ˈkwando ˈʎeɣa/
  I don't know when he or she arrives.

Spanish uses saber /saˈβeɾ/ for knowing facts. The Real Academia Española distinguishes this from conocer /konoˈseɾ/, which usually means knowing or being familiar with a person, place, or thing. That distinction matters when you want to be precise.

When to use No lo sé

No lo sé /no lo ˈse/ means I do not know it. The small word lo /lo/ refers to a specific fact, answer, or piece of information already under discussion.

Imagine someone asks:

• ¿Sabes cuál es la respuesta? /ˈsaβes kwal es la resˈpwesta/
  Do you know what the answer is?

A very natural reply is:

• No lo sé. /no lo ˈse/
  I don't know.

You can often use either No sé /no ˈse/ or No lo sé /no lo ˈse/. The difference is subtle: No sé /no ˈse/ is broader, while No lo sé /no lo ˈse/ clearly points back to the information mentioned.

John Butt and Carmen Benjamin explain in A New Reference Grammar of Modern Spanish that Spanish object pronouns often carry information English speakers would repeat as a noun. Here, lo /lo/ does that job efficiently.

Stronger ways to say you have no answer

Sometimes No sé /no ˈse/ sounds too plain. These alternatives show that you genuinely have no information, or that you are surprised by the question.

No tengo idea

No tengo idea /no ˈteŋɡo iˈðea/ literally means I have no idea. It is common throughout the Spanish-speaking world and is usually friendly, not rude.

It can sound more expressive than No sé /no ˈse/, especially with intonation:

• ¿A qué hora empieza? /a ke ˈoɾa emˈpjesa/
  What time does it start?

• No tengo idea. /no ˈteŋɡo iˈðea/
  I have no idea.

Ni idea

Ni idea /ni iˈðea/ is a short version meaning no idea or not a clue. It is casual and common in speech, text messages, and informal scenes in Spanish-language shows.

• ¿Quién llamó? /ˈkjen ʎaˈmo/
  Who called?

• Ni idea. /ni iˈðea/
  No idea.

Because it is clipped, avoid Ni idea /ni iˈðea/ in a job interview, a customer-service exchange, or a serious official conversation. Use No lo sé /no lo ˈse/ or No sabría decirle /no saˈβɾia ðeˈsiɾle/ instead.

No tengo ni idea

No tengo ni idea /no ˈteŋɡo ni iˈðea/ intensifies the statement: I have absolutely no idea. The word ni /ni/ adds force, much like not even in English.

This can be humorous with friends, but it may sound impatient if said flatly to someone seeking help. A warm tone changes everything.

Polite and professional alternatives

In Spanish, formality is not only about vocabulary. It also comes from tone, verb choices, and whether you use tú /tu/ or usted /usˈteð/. A softer phrase is particularly valuable when you are speaking with a client, teacher, older stranger, or official.

No sabría decirte

No sabría decirte /no saˈβɾia ðeˈsiɾte/ means I would not know how to tell you, or more naturally, I couldn't tell you. It uses the conditional form sabría /saˈβɾia/, which makes the uncertainty less blunt.

Use No sabría decirle /no saˈβɾia ðeˈsiɾle/ when addressing someone with usted /usˈteð/. The final pronoun changes, but the polite tone remains.

No estoy seguro or No estoy segura

No estoy seguro /no esˈtoj seˈɣuɾo/ is used by a man, while No estoy segura /no esˈtoj seˈɣuɾa/ is used by a woman. Both mean I am not sure.

This phrase is excellent when you have a possible answer but do not want to present it as certain:

• No estoy segura, pero creo que abre a las nueve. /no esˈtoj seˈɣuɾa ˈpeɾo ˈkɾeo ke ˈaβɾe a las ˈnweβe/
  I'm not sure, but I think it opens at nine.

Lo desconozco

Lo desconozco /lo ðeskonoˈsko/ means I am unaware of it. You may see it in formal emails, official statements, or administrative language.

In everyday conversation, it can sound overly stiff. Francisco Moreno Fernández, in Variedades de la lengua española, emphasizes that register varies not only between countries but also across social situations. A phrase that sounds normal in a formal report can sound distant at a family dinner.

Useful sentence patterns

Once you know No sé /no ˈse/, learn a few patterns rather than memorizing isolated lines. They allow you to respond naturally to dozens of questions.

Notice that Spanish does not need a word equivalent to English whether in most of these sentences. No sé si viene /no ˈse si ˈbjene/ simply means I don't know if he or she is coming.

Common mistakes English speakers make

Adding yo every time

Yo no sé /ʝo no ˈse/ is grammatical, but Spanish usually drops the subject pronoun. The verb ending already shows that the speaker is first person.

Use Yo no sé /ʝo no ˈse/ only for contrast:

• Yo no sé, pero Carlos sí sabe. /ʝo no ˈse ˈpeɾo ˈkaɾlos si ˈsaβe/
  I don't know, but Carlos does.

Confusing saber and conocer

Do not say No conozco /no koˈnosko/ when you mean you do not know an answer. Conocer /konoˈseɾ/ is for familiarity.

For example:

• No conozco Madrid. /no koˈnosko maˈðɾið/
  I do not know Madrid, meaning I have not experienced or visited it.

• No sé dónde está Madrid. /no ˈse ˈdonde esˈta maˈðɾið/
  I do not know where Madrid is.

Using No sé nada too casually

No sé nada /no ˈse ˈnaða/ means I know nothing. It can be a strong statement, especially when discussing a serious matter.

If you only mean that you lack one piece of information, choose No sé /no ˈse/ or No lo sé /no lo ˈse/. Spanish allows multiple negatives, so No sé nada /no ˈse ˈnaða/ is correct grammar, not a double-negative error.

Mistaking a blunt phrase for a neutral one

Yo qué sé /ʝo ke ˈse/ can mean how should I know or what do I know. Friends may use it playfully, but it can sound dismissive depending on tone.

Avoid it with strangers and in formal situations. If you are unsure, No estoy seguro/a /no esˈtoj seˈɣuɾo seˈɣuɾa/ is the safer choice.

Practice with real conversation

A good response does more than admit uncertainty. It keeps the exchange moving. Try these three-step replies:

1. No lo sé, pero puedo averiguarlo. /no lo ˈse ˈpeɾo ˈpweðo aβeɾiˈɣwaɾlo/
   I don't know, but I can find out.

2. No estoy seguro, ¿quieres que lo busque? /no esˈtoj seˈɣuɾo ˈkjeɾes ke lo ˈbuske/
   I'm not sure, do you want me to look it up?

3. Perdón, no sabría decirte. Quizás en recepción sepan. /peɾˈdon no saˈβɾia ðeˈsiɾte kiˈsas en resepˈsjon ˈsepan/
   Sorry, I couldn't tell you. Perhaps the reception staff know.

Watch Spanish-language scenes where characters ask for directions, make plans, or solve a problem. Pause after each uncertain response and repeat it with the same rhythm. This is especially effective when you use movies and TV to learn Spanish, because you hear how tone turns a simple No sé /no ˈse/ into concern, surprise, annoyance, or friendliness.

The phrase to remember

Start with No sé /no ˈse/. It is short, accurate, and natural in every Spanish-speaking country.

Then add three upgrades: No lo sé /no lo ˈse/ for a specific answer, No tengo idea /no ˈteŋɡo iˈðea/ for emphasis, and No sabría decirle /no saˈβɾia ðeˈsiɾle/ for formal politeness. Once these are automatic, you can handle uncertainty without freezing, then continue the conversation naturally with a Spanish goodbye when it is time to leave.