Municipality Kostanjevica na Krki, which is part of the Spodnjeposavska statistical region, measures 58 km2; this ranks it 119th among Slovene municipalities.
Statistical data for 2012 reveal the following:
In the middle of 2012 about 2,400 people (about 1,200 men and 1,200 women) were living in the municipality, which ranks Kostanjevica na Krki 170th among Slovene municipalities. The population density was 41 people per square kilometre, which was lower than the national average of 101 people per square kilometre.
The number of live births was higher than the number of deaths, which means that natural increase per 1,000 population in the municipality was positive. It was 2.1 (in Slovenia 1.3). The number of people who moved from the municipality was higher than the number of people who moved into the municipality, so net migration per 1,000 population in the municipality was negative. It was -0.4. The sum of natural increase and net migration per 1,000 population in the municipality was positive. It was 1.7 (in Slovenia 1.6).
The mean age of people in Kostanjevica na Krki was 41.6 years, which was lower than the national average (42).
As in most Slovene municipalities, in Kostanjevica na Krki the number of old people was higher than the number of young people: there were 118 people, aged 65 or more, per 100 people aged 0–14. This ratio shows that the value of the ageing index was the same as the national average. It also shows that the mean age of people in Kostanjevica na Krki is growing as fast as in Slovenia as a whole. Data by sex show that the ageing index for women was in all Slovene municipalities higher than the ageing index for men. In Kostanjevica na Krki – as in most Slovene municipalities – more women were 65+ years old than 14 or less; for men the situation was exactly the opposite.
Kostanjevica na Krki had 1 kindergarten. They were attended by 107 children or 85% of all children aged 1–5, which was more than the national average of 75%. In the school year 2012/2013 basic school in Kostanjevica na Krki was attended by about 190 pupils, while various upper secondary schools were attended by about 100 pupils. There were 60 students and 12 graduates per 1,000 people in the municipality; in Slovenia the averages were 47 per 1,000 and 10 per 1,000, respectively.
Among people aged 15–64 (i.e. working age population) about 60% were persons in employment (i.e. persons in paid employment or self-employed persons), which is more than the national average of 57%.
The registered unemployment rate was 12.1%, which is more than the national average (12%). In contrast to most Slovene municipalities, the same number of men as women were unemployed.
In Kostanjevica na Krki, average monthly gross earnings per person employed by legal persons were about 32% lower than the annual average of monthly earnings for Slovenia; and net earnings about 28% lower.
In 2012, there were 436 dwellings per 1,000 population. About 71% of dwellings had at least three rooms. Average size of dwellings in the municipality was 85 m2.
About every other person in Kostanjevica na Krki had a car (56 passenger cars per 100 population); cars in this municipality were on average 10 years old.
In 2012, 311 kg of municipal waste per person was collected in Kostanjevica na Krki, which is 16 kg less than on average in Slovenia.