AFR

AFR is a three-letter acronym that can refer to different concepts depending on the context. Among the most common usages are Annualized Failure Rate, Applicable Federal Rate, and Air-Fuel Ratio.

Annualized Failure Rate describes a reliability metric used to estimate the expected rate of failures in a product or component on a yearly basis. It is often derived from field failure data or modeled from distributions such as the Weibull distribution. AFR is used to compare reliability across designs, plan maintenance, and guide product improvements. Its interpretation depends on the data quality, testing conditions, and the time horizon of the study, and it may not capture all failure modes.

Applicable Federal Rate is a set of interest rates determined by the United States Internal Revenue Service for use in private loans, annuities, and some business transactions. Published monthly, AFRs are categorized into short-term, mid-term, and long-term rates and are used to determine minimum, or imputed, interest to prevent below-market lending. They influence gift and estate planning, pricing of intra-family loans, and certain financial arrangements where outside-market interest would otherwise apply.

Air-Fuel Ratio refers to the proportion by mass of air to fuel in an internal combustion engine. A stoichiometric gasoline engine operates near an AFR of about 14.7:1, meaning 14.7 parts air to 1 part fuel by mass. Deviations from this ratio affect engine performance and emissions, with lean mixtures (higher AFR) reducing fuel use but risking power loss, and rich mixtures (lower AFR) increasing fuel consumption and emissions. AFR is monitored by sensors and managed by the engine control unit to optimize efficiency and emissions.