The oldest calculator, the abacus, was invented in ancient Egypt(unknown date). The first Mechanical calculator, known as the Calculating clock, was invented by Willhelm Schickard in 1623. The first electronic desktop calculator were announced by the Bell Punch Co, in Uxbridge England in 1961. Finally, the first handheld computer was invented in 1980.
The first calculator dates back to 2700 BC with the invention of the Abacus, invented in Mesopotamia. In the 1940's and 1950's, the first mainframe computers were invented, which led towards the hand-held calculators we know today. In the mid-1960's, desktop calculators were coming to fruition, and in 1970, the first "Pocket" calculator was invented in Japan by Sanyo, called the ICC 0081.
Well the modern calculator with circuits was invented by William Seward Burroughs, while the first calculator (slide and rule) was invented by W. Oughtred (1574-1660). Nobody "discovered" the calculator in the contemporary sense. It was a natural outgrowth of continuous integrated circuit miniaturization.
The FIRST calculator was the abacus- made so long ago, we have no records of who invented it. Blaise Pascal created a mechanical calculator in1620, but the first successful calculator was Thomas de Colmar in France in 1820. Electronic calculators came after the creation of computers during WW 2. IBM and Sharp created some of the earliest electronic calculators.
The Curta calculator was the first handheld calculator. It was invented during WW2 by a prisoner in a Nazi concentration camp named Curta. The first model was intended as a gift for Hitler, but the war ended too soon Curta's were produced from about 1947 to 1976, when electronic handheld calculators killed Curta's market.