Which is correct, “I always work on Monday” or “I always work on Mondays”?
On Monday or on Mondays, on Tuesday or on Tuesdays, on Wednesday or on Wednesdays, on Thursday or on Thursdays, on Friday or on Fridays, on Saturday or on Saturdays, on Sunday or on Sundays?
Rules and Examples
RULE: Use the plural form of a day of the week when you talk about it in general, when the fact repeats.
INCORRECT: I always work on Monday.
CORRECT: I always work on Mondays.
Notice that the sentence contains a verb in the Simple Present and an adverb of frequency. Use a plural form of the name of the day of the week to show repetition.