I’ll Let You Know When in Spanish | Natural Ways To Say It

The most natural Spanish version is “te aviso cuando lo sepa,” while “ya te diré cuándo” works better when the date or time is the real point.

“I’ll let you know when” looks simple in English. In Spanish, it splits into a few different choices. The right one depends on what you’re promising to share: an update, a date, a time, or a final answer.

That’s why a word-for-word swap can sound stiff. If you want Spanish that feels normal in speech, text messages, and email, you need the version that matches the moment, not just the dictionary entry.

Why One English Line Has More Than One Spanish Match

English packs a lot into this one line. Sometimes it means “I’ll tell you once I have news.” Sometimes it means “I’ll tell you the exact time or date later.” Spanish tends to split those ideas instead of forcing one fixed phrase to do every job.

Use this simple split:

• Use avisar when you mean you’ll send an update: Te aviso cuando lo sepa.
• Use decir when the missing piece is the date or time: Ya te diré cuándo.
• Use a more formal line when the setting is work, service, or client-facing writing: Le aviso en cuanto tenga confirmación.

That small shift makes a big difference. “Te aviso” feels like “I’ll keep you posted.” “Te diré” feels like “I’ll tell you.” Both are correct. They just don’t land the same way.

Saying I’ll Let You Know When In Spanish Naturally

The most common everyday choice

Te aviso cuando lo sepa is the safest everyday option. It sounds natural, clear, and relaxed. You can use it with friends, family, coworkers, and most casual chats. It works well when you’re waiting on news and plan to pass that news along.

Say you’re waiting for a restaurant to confirm a booking. You could say, Te aviso cuando me respondan. If you’re waiting to hear back from a manager, Te aviso cuando sepa algo fits just as well.

When the missing piece is the exact date or time

Ya te diré cuándo sounds better when “when” itself is the answer you’ll give later. It points straight at the timing. You’re not promising a general update. You’re saying the date, day, or hour is still undecided.

This is the sort of line you’d use with plans: No sé qué día vamos; ya te diré cuándo. In English, that’s still “I’ll let you know when,” but Spanish likes the verb decir here.

Formal and polished options

In formal writing, le avisaré, le informaré, or le haré saber can work. Of those, le avisaré en cuanto tenga novedades is the most natural across a wide range of settings. Le haré saber is correct, though it can feel stiff in everyday speech.

If you write to a client, office, school, or service desk, this tone fits well. It sounds polite without turning wooden.

Spanish phrase	Best use	Natural English sense
Te aviso cuando lo sepa.	General updates in casual speech	I’ll let you know once I know.
Te aviso cuando sepa algo.	Waiting for news or a reply	I’ll tell you when I hear something.
Ya te diré cuándo.	Date or time still undecided	I’ll tell you when.
Luego te digo cuándo.	Relaxed, conversational planning	I’ll tell you later when it is.
Te aviso en cuanto sepa algo.	Prompt update promised	I’ll let you know as soon as I know.
Le aviso cuando tengamos confirmación.	Professional or formal writing	I’ll let you know when we have confirmation.
Cuando sepa algo, te aviso.	Same meaning, more emphasis on timing	When I know something, I’ll let you know.
Te digo cuando tenga la fecha.	The exact day matters	I’ll tell you when I have the date.

The Grammar Behind These Phrases

One reason learners get stuck here is the verb after cuando. In English, “when I know” sounds normal. In Spanish, when the action has not happened yet, the verb after cuando often shifts to the subjunctive: cuando sepa, cuando tenga, cuando podamos.

That’s why te aviso cuando lo sepa sounds right, while te aviso cuando lo sé sounds off in this context. The same pattern shows up in dozens of common lines. The RAE’s note on cuando points to this contrast.

Avisar and decir are not interchangeable in every case

Avisar leans toward “notify,” “tell,” or “alert,” depending on context. The RAE definition of avisar lines up with that idea of giving notice. So when you mean “I’ll update you,” avisar is a strong fit.

Decir is broader and more direct. If the missing detail is the answer itself, not the act of updating, decir often sounds cleaner. That’s why ya te diré cuándo feels so natural for plans.

What about “te haré saber”?

You may hear te haré saber, and it is valid Spanish. Still, it carries a more formal ring. In ordinary conversation, many speakers would lean toward te aviso or te digo. A literal line like te dejaré saber also appears in bilingual settings, mainly under English influence, but it does not sound as neutral across the Spanish-speaking world.

The same goes for structure. Spanish allows more than one pattern with avisar. The RAE usage note on avisar shows that both avisar que and avisar de que can be valid, though one may sound more natural depending on the sentence.

Situation	Best Spanish line	Why it fits
Waiting for a text back	Te aviso cuando me responda.	You’re promising an update.
Unsure what day to meet	Ya te diré cuándo.	The date itself is still unknown.
Work email to a client	Le aviso en cuanto tenga confirmación.	Polite and natural for work.
Family plans still up in the air	Luego te digo cuándo vamos.	Relaxed and conversational.
Urgent update promised	Te aviso en cuanto sepa algo.	Shows you’ll reply right away.

How Tone Changes The Choice

Casual speech

With friends or family, shorter is better. Te aviso, te digo luego, or ya te diré all sound easy and natural. Spanish often trims extra words when the context is already clear.

That means you do not always need the full English shape. A native speaker may simply say te aviso if both people already know what update is coming. The “when” is understood from the situation.

Work and formal writing

At work, clarity matters more than sounding fancy. Le aviso en cuanto tenga respuesta is clean and professional. Le informaré cuando disponga de la fecha is also fine, though it sounds more distant and official.

If you want neutral Spanish that travels well across countries, avisar is your safest bet. It is plain, direct, and easy to understand in a wide range of settings.

What to skip

Skip translations that cling too tightly to English form. Te dejaré saber cuándo may be understood, yet it often reads like a calque. If your goal is Spanish that sounds natural to the broadest audience, te aviso cuando lo sepa or ya te diré cuándo will serve you better.

A Simple Way To Pick The Right Version

If you only want one rule, use this:

• Choose te aviso when you’re promising an update.
• Choose ya te diré cuándo when the date or time is the missing piece.
• Use cuando sepa, cuando tenga, or similar forms after cuando when the action is still pending.
• Use a formal version like le aviso en cuanto tenga confirmación for work or client-facing writing.

So if you want one line that works in most real conversations, go with te aviso cuando lo sepa. If the real meaning is “I’ll tell you the time or date later,” switch to ya te diré cuándo. That choice sounds smoother, more natural, and much closer to how Spanish is actually spoken.