15. If there is a limit on the amount a donor can contribute to a political party during a non-election specific period, what is the limit?

"Maximum value of donation at annual level that a natural person may give to political entities for regular work shall not exceed ten average monthly salaries. Maximum value of donation at annual level that a legal person may give to political entities for regular work shall not exceed 30 average monthly salaries. Donations exceeding at annual level one average monthly salary are published. A political entity is required to publish each donation referred in paragraph 3 of this article on its website within eight days from the date the value of donation has exceeded the amount of one monthly average salary." 
Source: Article 10. law on financing political activities.

10 average monthly salaries for natural persons, 30 average monthly salaries for legal persons, per year.

To illustrate this better: in July 2023 (last statistical data available), the average monthly salary was 83.781 RSD (~ 710 EUR) – so the limit for natural persons would be 7100 EUR annually, and for legal persons 21.300 EUR annually for regular finances.

Additional remarks: Maximum amounts are the same for election campaign support – in a year of elections, a natural person can donate twice the maximum – one to regular finance of parties activities, and another to campaign of certain candidate/party list. The law frames these ceilings to calendar year only, regardless of how many elections are held.