Correct spelling


Correct spelling, explanation: months is a plural noun. It was created by adding the -s letter to the end of the root (month), so it’s a regular one. This word originates from Old English mōnath, of Germanic origin; it’s related to Dutch maand and German Monat, also to moon. You can’t spell months as monthes because the singular ends in a -h.

Definition of months:
noun (plural), periods of about four weeks
The siege lasted almost four months.
He’s returning to Africa tomorrow after six months in Europe.

Collocations with months:
Some most commonly used collocations include: past few months, and previous months.
The past few months have been difficult for me.
Our company began to achieve better results compared to previous months.

Incorrect spelling


Incorrect spelling, explanation: the word monthes doesn’t exist and this form should be avoided. The word-formation basis is correct, but the suffix is not. The right form is months with the -s. Why? Because the singular doesn’t end in –s, –sh, –ch, –x, or –z (for those letters you add -es). Try to remember that monthes is just a misspelling and you can’t write this word like that.