John Gill Reformed Baptist @doctorgill

And when he had agreed with the labourers for a penny a day,.... These labourers were of that sort that were called , "hired for a day"; concerning whom is the following rule (q): "he that is hired for a day, may demand it all the night; and he that is hired for a night may demand it all the day: he that is hired...

Albert Barnes Presbyterian @notesbybarnes

Verse 2. A penny a day. The coin here referred to was a Roman coin, equal in value to about 14 cents, [about 7d.] The original denotes the Roman denarius, δηναριου a silver coin, which was originally equivalent to ten asses, (a brass Roman coin,) whence its name The consular denarius bore on one side a head of Rome, and an X or a star...

Jamieson-Fausset-Brown Reformed @jfbcommentary

And when he had agreed with the labourers for a penny--a usual day's hire. he sent them into his vineyard.