Days of the week in Spanish are not capitalized. Always use el before a day of the week (except when stating what day it is). › Ex. Hoy es martes. To make sabado and damingo plural, add –s. To say on Monday, on Tuesday, etc. Use el lunes, el mantes. To say on Mondays, on Tuesdays, etc. Use los lunes, los, martes. Los lunes, vamos al colegio. And last the days of the week always start with Mondays and end with Sundays.