Unlike inflation, demurrage gradually reduces only the value of currency held: it functions as a negative interest (a tax) on currency held versus inflation that also reduces the value of savings or retirement funds and increases CPI. A positive interest rate is a subsidy. Both inflation and demurrage reduce the purchasing power of money held over time, but demurrage does so through fixed regular fees, while inflation does it in a variety of ways. Inflation is certainly not always everywhere a monetary phenomenon. Inflation is not always easy to predict and it does not stay fixed through time, but the level of demurrage is fixed by the government.