A day-fine, day fine, unit fine or structured fine is a unit of payment for a legal fine which is based on the offender's daily personal income. It is intended as a punishment financially equivalent to incarceration for one day without salary, scaled to equal impacts on both high- and low-income offenders. An analogy may be drawn with income tax, which is also proportional to income, or even levied at higher rates for higher incomes.

A fine or mulct is a penalty of money that a court of law or other authority decides has to be paid as punishment for a crime or other offense. The amount of a fine can be determined case by case, but it is often announced in advance.