in advance vs ahead

in advance and ahead both are adjectives.

Word	Noun	Adjective	Verb	Adverb
in advance	No	Yes	No	Yes
ahead	No	Yes	No	Yes

As adverbs, in advance and ahead are synonyms defined as:

Other synonyms of in advance include beforehand.

in advance (adjective)	ahead (adjective)
situated ahead or going before	having the leading position or higher score in a contest

in advance (adverb)	ahead (adverb)
ahead of time; in anticipation	at or in the front
	ahead of time; in anticipation
	in a forward direction
	leading or ahead in a competition
	to a different or a more advanced time (meaning advanced either toward the present or toward the future)
	to a more advanced or advantageous position
	toward the future; forward in time