Explain how second-round effects and core inflation affect monetary policy decisions. Illustrate with the RBI MPC's recent change of stance.

Under the amended RBI Act, 1934, the Monetary Policy Committee (MPC) must keep headline CPI inflation at 4% ± 2% [2]. The repo rate cannot fix supply shocks, so the MPC usually looks past a first price spike. It acts when that spike spreads to other prices. Second-round effects and core inflation are the signals it watches for that spread.

Second-round effects and policy choices

• Meaning: A shock in oil or food prices raises wages, transport costs and input costs. Inflation then becomes broad-based.
• First round: The MPC can look through these spikes, because food and fuel prices "do not react to monetary policy" [3].
• Second round: Inflation is now driven by demand and expectations, so tightening works.
• Expectations: Households' one-year inflation expectations move closely with headline inflation (correlation 0.73) [4]. If the MPC delays, a wage–price spiral becomes more likely.

Core inflation as a diagnostic

• Core inflation (CPI excluding food and fuel) shows persistent underlying pressure. If core rises, the shock is spreading.
• Limit: Food makes up about 46% of India's CPI basket, and headline and food inflation move together (correlation 0.93) [4]. India therefore targets headline inflation and uses core only as a guide [3].

Illustration: October 2026 MPC

West Asia conflict → costlier crude → fuel and input costs
        → core inflation 3.9% → 4.2%
        → share of CPI items above 4%: 20% → 37%
        → repo +25 bps; stance: neutral → calibrated tightening

Flowchart: how an imported shock spreads and the MPC's response

• Decision: The MPC unanimously raised the repo rate to 5.5% and changed its stance to calibrated tightening [1].
• Evidence of spread: Core inflation was 4.2% in August 2026, and 37% of CPI items were rising faster than 4%. Headline inflation is projected to touch 6% in Q3 [1].
• Counterpoint: Without precious metals, core inflation was only 2.9% [1]. Gold, not domestic demand, pushed the core figure up.
• Dissent: External members Nagesh Kumar and Ram Singh opposed only the change of stance. They warned it could signal an extended cycle of rate hikes and undo growth-supportive fiscal and monetary policies [1].

The October 2026 decision shows that the MPC raises rates when a supply shock starts spreading to other prices, not when the shock first appears. Wide diffusion was the strongest sign of that spread. The core figure was less reliable because gold inflated it. The way forward is for the MPC to report core inflation without gold, tie its stance to clear conditions, and coordinate fuel taxes with the government. That keeps price stability credible while protecting growth, as the 2016 framework intends.