ELKA (Bulgarian: ЕЛКА) is a Bulgarian brand of electronic calculator, developed by the Central Institute for Calculation Technologies(bg) and built at the Elektronika factory in Sofia. The name is a contraction of ЕЛектронен КАлкулатор, or "electronic calculator", and the word elka has, by extension, become the generic name for a calculator.
The first model, the ELKA 6521, was introduced in 1965, and used germanium transistors.  It weighed 8.5 kg and was the first calculator in the world to include a square root function. Its developers – Lyubomir Antonov, Petar Popov and Stefan Angelov, were the first scientists in the field of electronics to win the highest honour in Bulgaria at the time, the Order of Georgi Dimitrov. 
Later models were the ELKA 22 (with a luminescent display) and ELKA 25, (with an in-built printer) also in 1965. The latter two models proved successful and in 1967 begin being produced at the Factory for Organizational Technology in Silistra.
In 1969, the Scientific research, study and design institute for electronic calculators was founded specifically for the design of calculators. This developed the lighter and more portable, but still relatively large, ELKA 40 and ELKA 50 models and series.  The ELKA 1300 had a similar outward appearance to the 50 series, but was battery-powered. Meanwhile, the ELKA 77 was the first electronic cash register. 
The first pocket model was the ELKA 101, introduced in 1974. This was the first in a large series, including the scientific ELKA 135. Other models in the 100 series included the ELKA 103, 105, 131 and 130M. These were all designed with export in mind, so all writing on them is in Latin script. The 100 series came in three bright colours – orange, green, and yellow, and their displays could be either red or green. 
As of 2013 the factory in Silistra, now named "Orgatehnika", still produces ELKA calculators.