Learn Hardcore Spanish (Spain): A medida que avanza el día, me siento más tranquilo.

Breakdown of A medida que avanza el día, me siento más tranquilo.

What does a medida que mean, and is it a fixed expression?

Yes. A medida que is a fixed expression meaning as, as/while, or more precisely in proportion as / gradually as.

In this sentence, it shows that one thing changes progressively alongside another:

It is very common in Spanish for describing gradual change.

Why is it avanza?

Because the subject is el día, which is third person singular.

So the verb avanzar is conjugated as:

Here, the day is what is advancing or moving forward, so Spanish uses avanza.

Why does Spanish say el día advances? That sounds strange in English.

It is a normal Spanish way of speaking. Spanish often uses verbs like avanzar, pasar, or transcurrir with time expressions.

So these are all natural:

In English, we usually say the day goes on or the day passes, but Spanish can literally say the day advances.