overestimate

/OW0 V ER0 EH1 S T AH0 M EY0 T/
noun
  1. 1

    An estimate that is too high.

verb
  1. 1

    To judge or calculate too highly.

    โ€œI overestimated the number of attendees, and bought far too much food for the party.โ€

Source: https://en.wiktionary.org/wiki/overestimate