What time of day do you say buenos días?

From waking until early afternoon. In most of Latin America buenos días runs until about 13:00, when buenas tardes takes over. In Spain the boundary is later, typically 14:00 or 15:00, because lunch is the social anchor and lunch is late. Before about 06:00 the greeting starts to feel oddly chipper and you would more likely just nod; after lunch on either side of the Atlantic, switch to buenas tardes.

Is it buenos días or buen día?

Both are correct and the RAE accepts both. Buenos días (plural) is the Spain default and the textbook answer. Buen día (singular) is standard in Argentina and Uruguay and is widely used as the standard WhatsApp, SMS and email opener across much of Latin America. The plural is a fossilised elliptical from que tengas buenos días; the singular is the same construction reanalysed. Neither is more correct, despite what Spanish prescriptivists sometimes claim.

Should I respond with buenos días or with thank you?

Echo the same phrase back. If someone says buenos días, you say buenos días. The English habit of replying with thanks or with good morning to you is the single most consistent foreign-learner tell. Spanish reciprocation is symmetrical: the greeting and the response are the same words. If you want to add a return marker, y a ti (informal) or y a usted (formal) is the standard tag.

How do you say good night in Spanish to wish someone goodnight before sleep?

Buenas noches works for both the evening greeting (hello, after dusk) and the farewell before sleep. There is no separate goodnight word the way English splits good evening and good night. If you want to be more specific as a sleep farewell, que descanses (informal, may you rest) or que duermas bien (sleep well) are common follow-ups. Hasta mañana (until tomorrow) is the other standard close.

How to Say Good Morning in Spanish

The default answer is buenos días. Two words, plural noun, accent on the í. It is the standard morning greeting across every Spanish-speaking country and the safe answer in any register from a bakery counter to a board meeting. The fuller picture is a four-slot times-of-day system (buenos días, buenas tardes, buenas noches, plus the shortened buenas), with transition times that differ between Spain and Latin America, and a WhatsApp / email register where buen día has quietly become standard across much of the Americas. For the broader greeting cluster - hola, qué tal, regional casual openers - see how to say hello in Spanish. This article is the dedicated piece on the times-of-day system.

The four times-of-day greetings

Time window	Greeting	Literal meaning	Doubles as farewell?
Wake to ~13:00 (LatAm) / 14:00-15:00 (Spain)	Buenos días	Good days	No
Lunch boundary to dusk	Buenas tardes	Good afternoons	Yes (afternoon goodbye)
Dusk to sleep	Buenas noches	Good nights	Yes (evening + bedtime)
Any time (casual)	Buenas	Goods	Yes (casual greeting only)

Pronunciation notes:

Buenos días: BWE-nos DEE-as. The í carries the stress and the accent mark is not optional in writing.
Buenas tardes: BWE-nas TAR-des.
Buenas noches: BWE-nas NO-ches.
Buenas: BWE-nas, on its own, with a slight rising tone.

Note the gender flip: días is masculine (buenos días) but tardes and noches are feminine (buenas tardes / buenas noches). Two of the three trip learners on the agreement; just memorise the pair.

The asymmetry worth flagging is buenas noches. English splits good evening (greeting) and good night (farewell before sleep). Spanish does not. Buenas noches is both. You greet someone at 21:00 with buenas noches and you say buenas noches to your partner as you turn out the light. The context disambiguates and Spanish speakers do not feel the lack of a separate word.

The transition times: Spain vs Latin America

The clock-time difference between Spain and Latin America is a real, documented divergence rather than a fudge. The Spanish lunch culture pushes the morning greeting later:

Spain: buenos días runs until lunch, which typically sits between 14:00 and 15:30. Saying buenos días at 14:30 in Madrid is normal. The bakery encounter that opens this article happened at 13:45 and the baker was already on buenas tardes, which is on the early side of the Spanish range but not unusual.
Argentina, Mexico, Colombia, Peru, Chile: most of Latin America switches around 13:00, anchored to a midday lunch closer to the British pattern. Buenas tardes from 13:00 onwards is the norm.
Buenas noches: starts at dusk in both regions, which means it shifts seasonally. June in Madrid, dusk is 21:30 and buenas noches starts late; December, dusk is 18:00 and buenas noches starts after work.

The practical rule for travellers: if you do not know whether you have crossed the boundary, use buenas and let the listener fill it in. It is the universal fallback and it cannot be wrong.

Buenas: the shortened all-purpose version

In casual Spanish across every region, buenas on its own works as a greeting at any hour. It is the contraction of buenas tardes or buenas noches with the noun dropped, and the listener fills in the appropriate slot based on the time.

Reading: slightly casual but never wrong. You can say buenas to the woman serving you in a café at 11:00, to the security guard at the office at 16:00, to the neighbour in the lift at 22:00. It is the single most useful greeting move for foreign learners because it removes the entire time-of-day decision. The only context where it sounds wrong is a formal written opener (an email to a client, a job application), where the full buenos días or buenas tardes is expected.

Note the form: buenas is always plural and always feminine, regardless of whether you would have completed it as buenas tardes or buenas noches. You do not say buenos on its own.

The plural form: why buenos días is plural

A question every learner asks: why "good days" rather than "good day"? The accepted explanation, supported by the RAE, is that the phrase is a fossilised ellipsis. The original construction was que tengas buenos días (informal) or que tenga buenos días (formal): "may you have good days". The verb and the subjunctive marker dropped over time, leaving only the object phrase, but the plural noun stuck.

The same elliptical history sits behind buenas tardes, buenas noches and several other set phrases that look syntactically odd at first glance. The Diccionario panhispánico de dudas accepts both buenos días and buen día as standard, with a note that the plural is more common in Spain and the singular more common in parts of Latin America. Neither is incorrect.

Email and WhatsApp register

This is where most learners get it wrong, because the textbooks stop at the spoken form. The written register diverges by region:

Spain: buenos días opens emails and WhatsApp messages. Formal business email opens with Estimado/a Name followed by buenos días or buenas tardes. A morning WhatsApp to a colleague opens with buenos días.
Argentina, Uruguay: buen día (singular) is the standard email and WhatsApp opener. Hola, buen día is the casual version; buen día, Name is the slightly more formal one. Buenos días is understood but reads as Spanish-from-Spain.
Mexico, Colombia, Peru, Chile: a mixed picture, with both forms in circulation. Buen día is widely accepted as the WhatsApp standard; buenos días is more common in formal business email.

Four concrete openers learners can lift directly:

Casual WhatsApp (Spain): "Buenos días! Una pregunta rápida sobre la reunión de mañana."
Casual WhatsApp (Argentina): "Buen día! Te molesto con una pregunta sobre la reunión de mañana."
Business email (Spain): "Estimada María, buenos días. Le escribo para confirmar..."
Business email (Mexico): "Hola, María. Buen día. Le escribo para confirmar..."

The substitution is mechanical once you know the regional default. The mistake learners make is defaulting to the textbook buenos días everywhere, which reads in Buenos Aires the way "good morrow" would read in Manchester.

Regional variations

Beyond the Spain / LatAm split, a few country-specific moves worth picking up:

Argentina: buen día is the unmarked standard, both spoken and written. The reciprocation rule applies identically (echo buen día back, do not translate). Combined with the vos pronoun and the Rio Plata accent, this is one of the clearest regional registers.
Mexico: buenos días remains common in speech, buen día has gained ground in writing. The diminutive buenos diítas appears in very casual speech, particularly between women and in service contexts; it is warm rather than infantilising. Buenas tardecitas is the parallel afternoon diminutive in some regions.
Colombia: usted is used between close friends and even within families, which affects the greeting follow-up (buenos días, ¿cómo está usted? rather than the tu version). The greeting itself does not change.
Spain (Andalusia, the south): the shortened buenas is used heavily, even more than in Madrid or Barcelona. The final s on buenos and buenas tends to be aspirated or dropped, so what you hear is closer to "bueno" or "buena".
Chile: standard buenos días, with the heavy Chilean accent compressing the vowels. Buen día is rarer than in Argentina but present.

How to respond when someone greets you with buenos días

The single most important cultural rule: reciprocate the same phrase. If the baker says buenos días, you say buenos días. If the receptionist says buenas tardes, you say buenas tardes. The Spanish reciprocation is symmetrical, not transactional.

Three things English speakers do that read as foreign:

Translating the English construction: "good morning to you" becomes buenos días a usted or buenos días para usted. Both are technically intelligible but neither is what natives say. Just echo the phrase.
Replying with thanks: gracias, igualmente. Not wrong as a follow-up to a wish (que tengas un buen día → gracias, igualmente), but as a response to a bare greeting it skips the reciprocation step.
Adding "too": the English habit of marking the reciprocation with "too" or "as well" has no Spanish equivalent. The repetition itself is the reciprocation.

The standard return tags:

Y a ti (informal): "and to you". Buenos días, y a ti.
Y a usted (formal): "and to you". Buenos días, y a usted.
Igualmente (mutual): "likewise". Standard after wishes (que tengas un buen día → igualmente) rather than after bare greetings.

The reciprocation is automatic for natives, which is what makes it slow to internalise for learners. Drill it the same way you drill the conjugation tables: every time the input is a time-of-day greeting, the output is the same time-of-day greeting back.

Cross-links

How to say hello in Spanish covers the broader greeting cluster including hola, qué tal and regional casual openers.
Spanish phrases for the restaurant covers the service-counter register where buenos días and buenas tardes show up most frequently for travellers.
The Spanish pillar covers the wider adult-learner approach to Spanish.
Top 100 Spanish verbs covers the verb frequency list that pairs with this greeting vocabulary.
Spanish vocabulary by CEFR covers the staged vocabulary curriculum that times-of-day greetings sit at the front of.

How to Say Good Morning in Spanish: Buenos Días and the Times-of-Day Greetings