Theoretically, radiocarbon techniques have the ability to date samples to around 75,000 years, but the working threshold of reliable dating is around 50,000 years.
After 5,730 years, half (or 50 carbon-14 atoms) would remain.
The level of atmospheric C is not constant due to human activity, in part because of human combustion of fossil fuels and in part because of above-ground testing of the largely defensive weapon of the thermonuclear bomb.
Therefore dates must be calibrated based on Radiometric dating in general, of course, poses a huge problem for people who believe that the universe is 6000-odd years old.
Imagine a large swimming pool into which one drop of red ink falls each year.
The water dilutes the ink so much that even after a few thousand years very little pinkness can be seen in the pool.