19. If there is a limit on the amount a donor can contribute to a candidate, what is the limit?

14.(3) The amount of cash aid by each individual to a candidate, for each voting, may not exceed one month of gross salary of public servant actually paid within the scope of financial rights. [...]
Source: Article 14 (3), Presidential Election Law, 2012

Source: Law on Political Parties, 1983 (amended 2018)

Source: Law on Basic Provisions of Elections and Voter Registers, 1961 (amended 2018)

Circular of the Supreme Board of Election, April 30, 2018,  see http://www.ysk.gov.tr/doc/karar/dosya/77591/2018-335.pdf

The limit applies only to presidential candidates.There are no specific regulations regarding donations to candidates in other types of elections. 

The natural persons can contribute to the presidential candidate no more than one month of gross salary of a public servant. This refers to the groos salary of the undersecretary of the Prime Ministry under current system. According to the Circular of the Supreme Board of Election issued on April 30, 2018, the upper limit for donations to presidential candidates is 13,916,00 TRY.