How can the fertility rate be below 2 but the number of births is greater than deaths (South Korea)? I read an article published in 2020 which claimed that the South Korean population had declined "for the first time", the number of deaths (~300,000) outpacing births (~275,000). However, this would seem to be mathematically impossible because the birth rate has been below 2 in South Korea for decades (see chart below from World Bank). How is it even remotely possible?

Update: Based on one answer there is the idea that the increase in life expectancy could be an explanation. This seemed improbable to me originally, so I didn't consider it. But in any case, let's consider it:

So we see the life expectancy has increased from say 80 to about 82 apparently between 2010 to the present time, while the birth rate has been well below 2 that whole time. So, I guess I don't know the math of this. How do you compute birth rate vs life expectancy?

The other factor that can affect the birth rate is the age of women when they have children. According to this UN document Potential impact of later childbearing on future population, factors such as increased access to higher education and increased uptake of professional careers lead to women not only having fewer children but having their first child at an older age. This results in an increasing time between generations and thus a lower birth rate.
