Learn Hardcore Spanish (Spain): No quiero olvidar tu cumpleaños otra vez; por eso lo apunto ya en mi agenda y te escribiré una carta. - I don’t want to forget your birthday again; that’s why I’m writing it down in my planner already and I will write you a letter.

Lo is the direct object pronoun meaning “it” for a masculine singular noun. Here it refers to tu cumpleaños (birthday), which is grammatically masculine: el cumpleaños. If you were referring to a feminine noun like la fecha (de tu cumpleaños), you’d use la: “Por eso la apunto en mi agenda.”

What nuance does "ya" add in "lo apunto ya"?

Ya often means “already,” but here it conveys “right now/without delay.” It signals immediate resolution: “I’m putting it in my planner right now (so I don’t forget).” Alternatives: ahora mismo, enseguida, ya mismo.

Why is there a semicolon before "por eso"? Could I use a period or a comma instead?

The semicolon links two closely related independent clauses (reason → consequence) more tightly than a period and more cleanly than a comma. You could also write:

Period: “... otra vez. Por eso, lo apunto ...”
Comma + coordinating connector: “... otra vez, así que lo apunto ...” All are correct; the semicolon is a stylistic choice.

Should there be a comma after "por eso"?

It’s common and recommended to write a comma after connective adverbs like por eso when they begin a clause: “...; por eso, lo apunto ...” You will often see it omitted in informal writing; with the semicolon, including the comma improves readability.

Is "No quiero olvidar" correct, or should it be "No me quiero olvidar de"?

Both are correct:

Olvidar algo (transitive): “No quiero olvidar tu cumpleaños.”
Olvidarse de algo (pronominal): “No me quiero olvidar de tu cumpleaños.” / “No quiero olvidarme de tu cumpleaños.” Choose based on style; the pronominal form is a bit more colloquial. Don’t say “olvidar de” without the reflexive.

Why is it "tu" without an accent, not "tú"?

Tu (no accent) is the possessive adjective “your.” Tú (with accent) is the subject pronoun “you.” Here we need “your birthday” → tu cumpleaños.

Why does "cumpleaños" end in -s if it’s singular? What’s its gender?

Cumpleaños is an invariable noun ending in -s; it can be singular or plural depending on the article:

Singular: el cumpleaños (masculine)
Plural: los cumpleaños (e.g., “all the birthdays”) There’s no accent mark on the vowels; the tilde is only on ñ.

Can I move "otra vez" elsewhere? Is "No quiero volver a olvidar..." better?

Yes, you can vary the placement:

“No quiero olvidar otra vez tu cumpleaños.”
“No quiero volver a olvidar tu cumpleaños.” (very natural)
“No quiero olvidar tu cumpleaños de nuevo.” All are fine; volver a + infinitive emphasizes the repetition.

What does "apuntar" mean here? Could I say "anotar"?

Here apuntar means “to write down/jot down.” Anotar is a near-synonym and equally correct: “Por eso lo anoto en mi agenda.” Don’t confuse apuntar a (to aim/point at) with apuntar en (to write down in).

Where can the pronouns go? Is "ya lo apunto" different from "lo apunto ya"? What about "apuntarlo ya"?

With a conjugated verb, the clitic goes before it:

Ya lo apunto / Lo apunto ya (both fine; ya before or after slightly shifts emphasis) You attach the pronoun only to an infinitive, gerund, or affirmative command:
Infinitive: “Voy a apuntarlo ya.”
Gerund: “Estoy apuntándolo ya.”
Command: “Apúntalo ya.”

Why "te escribiré" and not "voy a escribirte" or "te escribo"?

Te escribiré (simple future) often expresses a promise/commitment.
Voy a escribirte suggests a planned near future.
Te escribo (present) can refer to a scheduled/near-future action in context. All are acceptable; the nuance is intention vs imminence.

Is "te" the direct or the indirect object in "te escribiré una carta"?

Te is the indirect object (“to you”), and una carta is the direct object (the thing written). With third person: “Le escribiré una carta a Juan.”

If I replace "una carta" with a pronoun, what is the order?

Indirect before direct:

“Te la escribiré.” (I’ll write it to you.) With third person, remember le/les → se before lo/la/los/las:
“Se la escribiré (a Juan).” Not “le la.”

Would Spaniards really say "una carta" for a birthday? What about "card" or "email"?

Una carta is a letter on paper (still fine, a bit traditional). For a birthday card, say una tarjeta (de cumpleaños). For email: un correo (electrónico) or simply un email.

Is "en mi agenda" the right preposition? Can I say "a mi agenda"?

Use en: “apuntarlo en mi agenda.” A would be incorrect here. In Spain, agenda is your personal planner/diary. You could also say en el calendario (on the calendar).

Any quick pronunciation tips for tricky words here?

Cumpleaños: the ñ sounds like “ny” in “canyon” (cum-ple-AN-nyos).
Escribiré: stress the last syllable (es-cri-bi-RÉ).
Quiero: the “qu” is like “k” (KYE-ro). The “ll” in cumpleaños isn’t present; but in words with “ll,” most Spaniards pronounce it like “y.”

Is the mix of present and future tenses normal: "lo apunto" + "te escribiré"?

Yes. Present for what you’re doing now; future for a later promise. It’s a natural combination.

How would this change with formal address (usted)?

“No quiero olvidar su cumpleaños; por eso lo apunto ya en mi agenda y le escribiré una carta.” Use su (your, formal) and le (to you, formal).

Could I drop "por eso" and use "así que" or "por lo tanto"?

Yes:

Así que (more colloquial): “...; así que lo apunto ...”
Por lo tanto (more formal): “...; por lo tanto, lo apunto ...” Por eso ≈ “that’s why/therefore,” neutral and very common.

Can I use "porque" instead of "por eso"?

Not with the same structure. Porque introduces the cause; por eso introduces the consequence. You’d need to flip the order:

Cause first with por eso: “No quiero olvidar ...; por eso lo apunto ...”
Cause with porque: “Porque lo apunto en mi agenda, no olvidaré tu cumpleaños.” (less natural here as a stand‑alone statement)

Can I say "ya te escribiré una carta"?

Be careful: Ya te escribiré often means “I’ll write to you later (eventually),” sometimes even “Don’t worry, I’ll get around to it.” In your sentence, te escribiré (without ya) is a clearer promise.