Real Business Cycle Model

The Real Business Cycle model emerged from Kydland and Prescott (1982) and Long and Plosser (1983) as a direct challenge to the Keynesian consensus that business cycles require demand-side stories. Their argument was radical for the time: a competitive economy hit only by technology shocks, with no market failures and no monetary frictions, could replicate the broad comovement patterns in U.S. macro data. The 1982 paper earned Kydland and Prescott the 2004 Nobel Prize.

The core mechanism is intertemporal substitution. When productivity rises, the return to capital and the real wage both increase. Households respond by working more and saving more, amplifying the initial shock through capital accumulation. Because adjustment is entirely real - no sticky prices, no monetary policy, no financial frictions - the RBC model isolates the supply-side propagation channel in its purest form.

Central banks and research departments still use RBC as a calibration benchmark. The Federal Reserve Bank of Minneapolis, where much of the early work happened, treats it as the baseline against which nominal and financial frictions are measured. Every New Keynesian, TANK, and HANK model in this family can be read as 'RBC plus friction X.' The model also anchors graduate macro coursework worldwide as the first dynamic stochastic general equilibrium structure students solve.

The main extensions since the 1980s include variable capacity utilization (Greenwood, Hercowitz, and Huffman 1988), labor indivisibility (Hansen 1985, Rogerson 1988), home production (Benhabib, Rogerson, and Wright 1991), and investment-specific technology shocks (Greenwood, Hercowitz, and Krusell 1997). Each extension tried to close specific gaps between the baseline RBC predictions and data - particularly the excess smoothness of hours and the low volatility of wages relative to output.

The model has three blocks: a representative household, a representative firm, and an exogenous government. The household maximizes expected discounted utility over consumption and leisure, choosing how much to work and how much to save each period. The firm rents capital and hires labor under Cobb-Douglas technology with a stochastic productivity process. The government absorbs resources through an exogenous spending process financed by lump-sum taxes.

Equilibrium is computed by combining the household's Euler equation (intertemporal consumption smoothing) and labor-leisure condition (intratemporal consumption-hours tradeoff) with the firm's factor-pricing conditions and the economy-wide resource constraint. Capital accumulation links periods through the law of motion $K_{t+1} =$ (1 - delta) $K_t + I_t$.

The model is solved by log-linearizing around a deterministic steady state and applying standard rational-expectations solution methods (Blanchard-Kahn, Uhlig, or Sims). The resulting policy functions express consumption, investment, hours, and output as linear functions of the state variables - capital and the two shock processes. Impulse responses trace how a one-standard-deviation innovation propagates over time.

The Federal Reserve Bank of Minneapolis and academic macro groups worldwide use RBC as the zero-friction benchmark. When a researcher adds sticky prices or financial frictions, the question is always 'how much does this friction change the RBC prediction?' The model's role is diagnostic rather than forecasting.

RBC is also the standard teaching vehicle for dynamic stochastic general equilibrium methods. Students learn steady-state computation, log-linearization, Blanchard-Kahn conditions, impulse response analysis, and variance decomposition on the RBC structure before encountering nominal frictions.

The model breaks down whenever the question involves monetary policy transmission, financial crises, distributional effects of policy, or any mechanism that requires a non-trivial role for nominal variables. If the central bank's interest rate matters for the answer, RBC is the wrong tool.