Burn rate is the rate at which a company is losing money. It is typically expressed in monthly terms. E.g., "the company's burn rate is currently $65,000 per month." In this sense, the word "burn" is a synonymous term for negative cash flow. It is also a measure of how fast a company will use up its shareholder capital. If the shareholder capital is exhausted, the company will either have to start making a profit, find additional funding, or close down.

Burn rate can also refer to how quickly individuals spend their money, particularly their discretionary income. For example, Mackenzie Investments commissioned a test to gauge the spending and saving behavior of Canadians to determine if they are “Overspenders.”

Burn rate is also used in project management to determine the rate at which hours (allocated to a project) are being used, to identify when work is going out of scope, or when efficiencies are being lost. The term is also used in biology, to refer to a person's basic metabolic rate; in rocketry, it refers to the rate at which a rocket is burning fuel; and in chemistry.