Gastar vs. pasar
In Spanish, both gastar and pasar can be translated as "to spend," but they are not interchangeable. The choice between them depends entirely on what is being spent: resources like money, or time.
Gastar
A2Use gastar when you are talking about spending or using up tangible or quantifiable resources. This most commonly includes money, but also applies to things like energy, fuel, supplies, or even patience.
No me gusta gastar dinero en cosas que no necesito.
(I don't like to spend money on things I don't need.)
Mi coche gasta mucha gasolina en la ciudad.
(My car spends (uses) a lot of gasoline in the city.)
Gastamos toda la tarde organizando los archivos.
(We spent the whole afternoon organizing the files.)
No gastes tus energías en una discusión sin sentido.
(Don't spend your energy on a pointless argument.)
¿Cuánto gastaste en la compra semanal?
(How much did you spend on the weekly groceries?)
Los niños gastaron todos los lápices de colores.
(The children used up (spent) all the colored pencils.)
Pasar
A1Use pasar exclusively when you are talking about spending time. It refers to how a period of time is occupied or how it goes by, whether it's an afternoon, a weekend, a vacation, or one's entire life.
Me encanta pasar tiempo con mis abuelos.
(I love to spend time with my grandparents.)
Pasamos el fin de semana en una cabaña en el bosque.
(We spent the weekend in a cabin in the woods.)
¿Cómo vas a pasar la Navidad este año?
(How are you going to spend Christmas this year?)
Él pasó toda su vida estudiando la historia antigua.
(He spent his entire life studying ancient history.)
Paso dos horas al día en el transporte público.
(I spend two hours a day on public transportation.)
Pasamos un buen rato charlando en el café.
(We spent a good while chatting at the café.)
Summary
The fundamental difference is simple: use gastar for spending resources (money, gas, energy) and use pasar for spending time (an hour, a vacation, a lifetime). Think of gastar as consuming something and pasar as time passing by.