Learn Hardcore Spanish (Spain): Antes de tomar una decisión de inversión, pienso en el riesgo y en mi tranquilidad. - Before making an investment decision, I think about the risk and my peace of mind.

Same subject → antes de + infinitive
- Antes de tomar una decisión, pienso…
- The person who “takes the decision” and the person who “thinks” is the same.
Different subject → antes de que + subjunctive
- Antes de que tomes una decisión, quiero hablar contigo.
- Before you make a decision, I want to talk to you.
- One subject “I want to talk”, another subject “you make the decision”.

Antes tomar is simply incorrect; you need de before an infinitive here. Antes de que tomo is also incorrect because after antes de que you need the subjunctive, so it must be antes de que tome/tomes/tomemos, etc., depending on the subject.

How do I know when to use antes de + infinitive and when to use antes de que + subjunctive?

Use this simple rule:

Same subject in both actions → antes de + infinitive
- Antes de comer, me lavo las manos.
- (I do both actions: eating and washing.)
Different subjects → antes de que + subjunctive
- Antes de que comas, quiero explicarte algo.
- (I explain; you eat.)

In your sentence:

Antes de tomar una decisión de inversión, pienso…
- The same person does both: “taking the decision” and “thinking”.
- So we use antes de tomar, not antes de que tomes.

Why is it una decisión de inversión and not una decisión de invertir?

Both are possible, but they mean slightly different things:

Una decisión de inversión
- Literally: an investment decision.
- Focuses on the type of decision (a decision in the field of investments).
- Very natural in financial or business contexts.
Una decisión de invertir
- Literally: a decision to invest.
- Focuses more on the action of deciding to invest.

So:

Antes de tomar una decisión de inversión…
- Before making an investment-related decision (e.g., which product, how much risk, etc.).
Antes de tomar la decisión de invertir…
- Before making the decision to invest (as opposed to not investing at all).

Your sentence talks about decisions within the realm of investing, so decisión de inversión is a good, natural choice.

Is decisión de inversión the only way to say “investment decision”?

No, there are several options, with slightly different nuances:

Una decisión de inversión – very standard and neutral in finance.
Una decisión sobre la inversión – more like “a decision about the investment” (more specific: about one particular investment).
Una decisión de invertir – “a decision to invest” (emphasis on the action of investing).
Una decisión inversora – grammatically possible but less common; sounds more technical or stylistic.

In everyday financial Spanish, decisión de inversión is one of the most common ways to say “investment decision.”

Why is decisión feminine (una decisión) and not masculine?

In Spanish, most nouns ending in -ción / -sión are feminine:

la decisión
la inversión
la organización
la información
la televisión

Therefore you must say:

una decisión de inversión (feminine article and adjective forms, when used)
not un decisión…

Why is it pienso en and not pienso sobre or pienso de?

The verb pensar changes meaning slightly depending on the preposition:

pensar en = to think about (to have in mind)
- Pienso en el riesgo. = I think about the risk / I consider the risk.
- This is the most common when you mean “I think about X”.
pensar sobre = to think about, usually in a more “analytical” or “discussion” sense; often in writing or formal speech.
- Pensó sobre el problema durante horas.
- Sounds more like “to reflect on / deliberate about”.
pensar de = to think of, as in giving an opinion.
- ¿Qué piensas de esta inversión? = What do you think of this investment?

In your sentence:

pienso en el riesgo y en mi tranquilidad
You mean “I consider / I think about these things.”
So pensar en is the correct and most natural choice.

Why is en repeated: en el riesgo y en mi tranquilidad? Could I just say pienso en el riesgo y mi tranquilidad?

Both are possible, but they feel slightly different:

pienso en el riesgo y en mi tranquilidad
- Repeating en is:
  - Very clear.
  - Slightly more formal or careful.
  - Preferred in writing.
pienso en el riesgo y mi tranquilidad
- Here en is understood to apply to both nouns.
- It’s acceptable and can sound a bit more fluid in speech.

Repeating the preposition is quite common in Spanish, especially if the two nouns are conceptually distinct (risk vs. peace of mind). The original version with repeated en is stylistically very natural.

Why is it el riesgo but mi tranquilidad? Could I say mi riesgo or la tranquilidad?

You could change the articles and possessives, but the meaning would shift:

el riesgo
- The risk (as a general or specific risk of that investment).
- Not necessarily “my personal risk”; it’s the risk level of the investment.
mi tranquilidad
- My peace of mind; something personal and subjective.

Alternatives:

mi riesgo:
- Would sound like the personal risk or exposure I have.
- Possible, but here the speaker likely wants to emphasize their inner peace as personal, not the risk.
la tranquilidad:
- More like “the peace/tranquility (in general)” or “the tranquility of the situation”.
- You lose the very personal nuance of mi.

So the original contrast:

el riesgo (objective factor of the investment)
mi tranquilidad (subjective, personal state)

is stylistically and semantically deliberate.

What exactly does tranquilidad express here? Is it the same as “calm” or “peace of mind”?

In this context, mi tranquilidad is best translated as my peace of mind:

It refers to how relaxed or stressed you feel about the investment.
It includes ideas like not worrying too much, being able to sleep well, not being anxious.

Other options:

mi calma – more like “my calmness”, less common in this exact financial sense.
mi paz mental / mi paz de espíritu – closer to “peace of mind”, but more expressive or literary.

Tranquilidad is the usual, natural word to talk about how “at ease” you feel with a financial decision in Spanish.

Could I change the word order, like pienso en mi tranquilidad y en el riesgo? Does it sound different?

Yes, you can say:

Antes de tomar una decisión de inversión, pienso en mi tranquilidad y en el riesgo.

It is grammatically correct. The difference is one of emphasis:

pienso en el riesgo y en mi tranquilidad
- Slightly foregrounds the risk first, then your peace of mind.
pienso en mi tranquilidad y en el riesgo
- Puts a bit more emphasis on your tranquility as the first element.

In Spanish, as in English, changing the order at the end of the sentence can subtly change what feels more salient, but both are perfectly natural.