calculate (v.) Look up calculate at Dictionary.com
1560s, "to ascertain by computation, estimate by mathematical means," from Latin calculatus, past participle of calculare "to reckon, compute," from calculus (see calculus). Meaning "to plan, devise" is from 1650s; hence "to purpose, intend" and "to think, guess" (1830), both U.S. idioms. Replaced earlier calculen (mid-14c.), from Old French calculer. Related: Calculable.