MII is a minimum earnings floor used for social insurance calculations. If you declare less than the floor for your profession, contributions may still be based on the higher figure.
This hits couriers, part-time freelancers, and anyone with volatile income especially hard — you can owe more SI than your cash flow suggests.
TaxCalc CY compares your gross to profession-based MII thresholds and warns you when the floor applies, so you can budget before filing.