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 2013 reveal the following:
In the middle of 2013 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 102 people per square kilometre.
The number of live births was lower than the number of deaths, which means that natural increase per 1,000 population in the municipality was negative. It was -1.2 (in Slovenia 0.9). 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 -5.4. The sum of natural increase and net migration per 1,000 population in the municipality was negative. It was -6.6 (in Slovenia 1.1).
The mean age of people in Kostanjevica na Krki was 42.3 years, which was higher than the national average (42.2).
As in most Slovene municipalities, in Kostanjevica na Krki the number of old people was higher than the number of young people: there were 123 people, aged 65 or more, per 100 people aged 0–14. This ratio shows that the value of the ageing index was higher than the national average of 119. It also shows that the mean age of people in Kostanjevica na Krki is growing more rapidly than 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. It was attended by 109 children or 85% of all children aged 1–5, which was more than the national average of 75%. In the school year 2013/2014 basic school in Kostanjevica na Krki was attended by about 190 pupils, while various upper secondary schools were attended by about 90 pupils. There were 50 students and 8 graduates per 1,000 people in the municipality; in Slovenia the averages were 44 per 1,000 and 9 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 12.7%, which is less than the national average (13.1%). As in most Slovene municipalities, more women than men were unemployed.
In Kostanjevica na Krki, average monthly gross earnings per person employed by legal persons were about 33% lower than the annual average of monthly earnings for Slovenia; and net earnings about 29% lower.
In 2013, there were 438 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 (57 passenger cars per 100 population); cars in this municipality were on average 10 years old.
In 2013, 385 kg of municipal waste per person was collected in Kostanjevica na Krki, which is 65 kg more than on average in Slovenia.