A calculation is a deliberate process that transforms one or more inputs into one or more results, with variable change.
The term is used in a variety of senses, from the very definite arithmetical calculation of using an algorithm, to the vague heuristics of calculating a strategy in a competition, or calculating the chance of a successful relationship between two people.
Statistical estimations of the likely election results from opinion polls also involve algorithmic calculations, but produces ranges of possibilities rather than exact answers.
To calculate means to ascertain by computing. The English word derives from the Latincalculus, which originally meant a small stone in the gall-bladder (from Latin calx). It also meant a pebble used for calculating, or a small stone used as a counter in an abacus (Latin abacus, Greekabax). The abacus was an instrument used by Greeks and Romans for arithmetic calculations, preceding the slide-rule and the electronic calculator, and consisted of perforated pebbles sliding on an iron bars.
Calculate comes from the Greek word Κάχληκα or gravel in English because Greeks used gravel for counting. In English, calculation involves numbers and the word usually connotes a simple process, but computation may be done by applying specific rules, with or without numbers, and the word is chosen for more complex tasks.
Calculation is a prerequisite for computation. The difference in the meaning of calculation and computation appears to originate from the late medieval period.