They don&#x27;t have to do mess around with face value.  Individuals and companies with billions of dollars in cash can&#x27;t really stick it in a mattress and ignore it.  They have to find storage, pay rent, heating&#x2F;cooling&#x2F;humidity control, security, etc.  That costs money.  Negative interest rates reflect that cost.<p>Security guards alone would cost round_up(24*7&#x2F;40) = 5 security guards assuming you only need a single guard (and they never get sick or take vacation), which at a loaded labor cost of at least $150k (low end) is $750k, which is 4% interest on $18.75m.  So, under $20m and you&#x27;re happy to pay the central bank the money to guard your cash.