The amount that an individual can spend consistently with being able to maintain the same level of spending in the future. This is a forward-looking concept, depending on expected levels of earned income, unearned income, and transfers from the state or other individuals due to be received over a whole lifetime of unknown length. Permanent income cannot be objectively measured, and is extremely difficult even to estimate. Some theories of consumption and liquidity preference suggest that consumption spending and desired money holdings depend on permanent rather than measured income.

• inelastic demand
• inelastic supply
• inequality
• inequality of incomes
• infant industry
• inferior good
• infinitesimal
• infinity
• inflation
• inflation accounting
• inflation-adjusted budget deficit
• inflationary gap
• inflationary spiral
• inflation tax
• inflection, point of
• inflow, capital
• information
• information agreement
• infrastructure
• inheritance tax
• initial conditions
• injections to the circular flow of incomes
• Inland Revenue
• innocent entry barriers
• innovation