Calculating profit on negative bond yields

In a world of negative interest rates where you need to pay money to hold bonds, we ask ourselves why do people still buy these bonds?



Well it appears that buying bonds can still be profitable at negative interest rates as long as the yield keeps going down. But there is a limit. Let's calculate this limit.



Here is the formula:

For example: if a 10 year bond has bond yields go down 1% per annum, you can make huge profits (around 10% profit). The question is, will bond yields go down 1% per annum? Is this sustainable?



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