Je mets ma ceinture avant de partir.

French makes a clear distinction between:

• mettre = to put on (the action of putting something on)
• porter = to wear (the state of having something on)

So:

• Je mets ma ceinture. = I put my seatbelt on. (action)
• Je porte une ceinture. = I am wearing a belt. (state)

Since the sentence describes what you do before leaving, the action verb mettre is the natural choice.

In French, possessive adjectives agree with the gender and number of the noun, not with the person who owns the object.

• ceinture is a feminine singular noun.
• The feminine singular form of my is ma.

So:

• ma ceinture (my belt)
• mon pantalon (my trousers) – because pantalon is masculine
• mes ceintures (my belts) – plural

Ceinture by itself literally means belt, but in context it is often understood as seatbelt, especially when talking about a car or leaving in a vehicle.

To be more explicit, French can also say:

• ceinture de sécurité = seatbelt

So:

• Je mets ma ceinture avant de partir.
  → in a driving context: I put my seatbelt on before leaving.
• Je mets ma ceinture avec ce pantalon.
  → in a clothing context: I put my belt on with these trousers.

In French, when avant is followed by a verb, you must use:

• avant de
  • infinitive

So:

• avant de partir = before leaving
• avant de manger = before eating
• avant de dormir = before sleeping

You cannot say avant partir; the de is required before the infinitive.

Both can translate as before leaving, but they are used differently:

1. avant de partir

   • Structure: avant de
     • infinitive
   • Subject of both actions is the same (I put on my belt, I leave).
   • Neutral, simple style.

2. avant que je parte

   • Structure: avant que
     • clause with subjunctive (je parte).
   • Used when the subjects can be the same or different, but it’s grammatically more complex.
   • Often used in more formal or elaborate sentences.

In your short sentence, avant de partir is the natural, simplest choice.

These three verbs aren’t interchangeable:

• partir = to leave, to depart (to go away from a place)
  
  • Je pars. = I’m leaving.
• aller = to go (to a place)
  
  • Je vais au travail. = I’m going to work.
• sortir = to go out, to go outside, to go out socially
  
  • Je sors ce soir. = I’m going out tonight.

In avant de partir, the idea is before leaving (this place / with the car), so partir fits best.

No, Je me mets ma ceinture is incorrect in standard French.

• mettre here is a normal (non‑reflexive) verb that takes a direct object: ma ceinture.
• The correct form is simply: Je mets ma ceinture.

Reflexive forms are used with verbs like:

• Je m’habille. = I get dressed.
• Je me lave. = I wash myself.

But with clothing or accessories, French usually uses a normal verb plus object:

• Je mets ma veste. = I put my jacket on.
• J’enlève mes chaussures. = I take my shoes off.

Yes, but it’s less personal and slightly different in nuance.

• Je mets ma ceinture.
  Emphasizes your belt/seatbelt, the one that belongs to or is assigned to you (your seatbelt in the car).

• Je mets la ceinture.
  More like I put the belt on, referring to a specific belt already known in the context. It can sound a bit more neutral or impersonal.

In practice, for a seatbelt or your belt, ma ceinture is the most natural everyday phrasing.

Mets is pronounced like [mɛ] (similar to “meh” in English, but shorter and tenser).

• The final -s in je mets is silent.
• In the present tense:
  • je mets → [mɛ]
  • tu mets → [mɛ]
  • il/elle met → [mɛ]

All three sound exactly the same when spoken.

Here is the full present‑tense conjugation of mettre:

• je mets – I put (on)
• tu mets – you put (on) (singular, informal)
• il / elle / on met – he/she/one puts (on)
• nous mettons – we put (on)
• vous mettez – you put (on) (plural or formal)
• ils / elles mettent – they put (on)

Watch the spelling changes in mettons / mettez / mettent, but the stem met- stays the same.

In both French and English, the present tense can express:

• a habit:
  
  • Je mets ma ceinture avant de partir.
    → I (always) put my seatbelt on before leaving.
• a general rule or routine:
  
  • Every time, this is what I do.

If you wanted to talk about a specific future occasion, you could say:

• Je mettrai ma ceinture avant de partir.
  = I will put my seatbelt on before leaving.

But as a general statement of habit, the present je mets is correct and natural.

You would use la (feminine singular direct object) to replace ma ceinture and put it before the verb:

• Je la mets avant de partir.
  = I put it on before leaving.

Position:

• Subject je
• Object pronoun la
• Verb mets
• Rest of the sentence avant de partir

You have a bit of flexibility, but not all orders sound natural.

1. Normal and most common:

   • Je mets ma ceinture avant de partir.

2. Also possible:

   • Avant de partir, je mets ma ceinture.

3. Unnatural / very awkward:

   • Je mets avant de partir ma ceinture. (sounds wrong or at least very clumsy)

So, keep avant de partir either at the beginning or at the end of the sentence, not in the middle of the verb and its object.