Municipality Kostanjevica na Krki, which is part of the posavska statistical region, measures 58 km2; this ranks it 119th among Slovene municipalities.
Statistical data for 2015 reveal the following:
In the middle of 2015 about 2,450 people (about 1,250 men and 1,200 women) were living in the municipality, which ranks Kostanjevica na Krki 170th among Slovene municipalities. The population density was 42 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 –0.4 (in Slovenia 0.4). 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 –14.3. The sum of natural increase and net migration per 1,000 population in the municipality was negative. It was –14.7 (in Slovenia 0.6).
The mean age of people in Kostanjevica na Krki was 42.5 years, which was lower than the national average (42.6).
As in most Slovene municipalities, in Kostanjevica na Krki the number of old people was higher than the number of young people: there were 114 people, aged 65 or more, per 100 people aged 0–14. This ratio shows that the value of the ageing index was lower than the national average of 123. It also shows that the mean age of people in Kostel is growing more slowly 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 the same.
In the school year 2015/2016 basic school in Kostanjevica na Krki was attended by about 200 pupils, while various upper secondary schools were attended by about 100 pupils. There were 40 students and 10 graduates per 1,000 people in the municipality; in Slovenia the averages were 39 per 1,000 and 9 per 1,000, respectively.
Among people aged 15–64 (i.e. working age population) about 62% were persons in employment (i.e. persons in paid employment or self–employed persons), which is more than the national average (58%).
The registered unemployment rate was 11.2%, which is less than the national average (12.3%). 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 34% lower than the annual average of monthly earnings for Slovenia; and net earnings about 10% lower.
In 2015, there were 415 dwellings per 1,000 population. About 71% of dwellings had at least three rooms. Average size of dwellings in the municipality was 85 m2.
Every other person in Kostanjevica na Krki had a car (57 passenger cars per 100 population); cars in this municipality were on average 10.9 years old.
In 2015, 361 kg of municipal waste per person was collected in Kostanjevica na Krki, which is 46 kg more than on average in Slovenia.