How many letters does the top answer for “a calculation that results in an estimate that is too high” have?

The most common answer is overestimate (12 letters).

Crossword clue: a calculation that results in an estimate that is too high

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

overestimate 12 letters wn-def

make too high an estimate of

overrating 10 letters wn-def

a calculation that results in an estimate that is too high

make too high an estimate of 50% similar → overestimate, overrate