-
Overestimate (verb)
To judge too highly.
“I overestimated the number of attendees, and bought far too much food for the party.”
-
Overestimate (noun)
An estimate that is too high.
-
Underestimate (verb)
To perceive (someone or something) as having a lower value, quantity, worth, etc., than what he/she/it actually has.
-
Underestimate (noun)
An estimate that is too low.
Wiktionary