GDP measures output, not legality
Gross domestic product (GDP) is an estimate of the value of goods and services produced within a country. Its purpose is to measure economic activity, so the legal status of a sale does not automatically determine whether it counts. Under shared national-accounting rules, countries including Italy, Spain, and the United Kingdom include estimates for some illegal markets, such as drugs and paid sexual services.
That does not mean every crime adds to GDP. A consensual sale of an illegal product can represent production and a purchase; theft, by contrast, transfers something already produced rather than creating new output. The distinction is about what economic activity occurred, not whether the law permits it.
Why count a market that is hidden?
Leaving an entire market out would make the total less complete and could make comparisons misleading. If an illegal market grew or shrank, GDP would miss that change even though goods or services were being produced and bought. Including estimates gives statisticians a more consistent picture of the economy across countries and over time.
Because these transactions are concealed, their value cannot be tallied from ordinary business records. National statisticians have to estimate it using indirect evidence and assumptions, so the figures are less directly observable than sales reported by legal firms. They are accounting estimates—not official approval of the activity, nor a measure of its social value. A black-market sale can raise measured output while still imposing serious costs on individuals and society.
