Unpacking India's GDP Data: Revisions, Methodology, and the Trust Deficit

What are the recent revisions to India's GDP data?

India's GDP data, particularly quarterly estimates, undergoes routine revisions as more comprehensive information becomes available. These revisions are a standard practice in national income accounting. Quarterly GDP numbers are initially compiled using a "benchmark-indicator approach," where high-frequency indicators such as crop production, cement production, finished steel consumption, and commercial vehicle sales guide the movement in estimates (Source: Indian Express Explained, Sep 5, 2026). In contrast, annual GDP estimates are based on actual output and financial data. As more 'actual' data, such as companies' financial results and MoSPI's surveys, becomes available for a specific quarter, the initial estimates are subsequently revised. For instance, the GDP growth for January-March 2026 (Q4 of FY26) was significantly revised upward from 7.8% to 8.6% due to the availability of more comprehensive data (Source: Indian Express Explained, Sep 5, 2026). Beyond these routine updates, changes to older data, including those going back to 2023-24, primarily stemmed from MoSPI's shift to a new indicator, the Producer Price Index (PPI), for adjusting nominal GDP to real GDP.

How has the methodology for calculating real GDP changed?

Calculating real GDP involves removing the effect of inflation from nominal GDP, a process known as deflation. Until recently, India primarily employed a "single deflation" method for most sectors, with exceptions for agriculture and mining and quarrying. In this approach, the value of both inputs and outputs for a sector, and its various subcategories, were adjusted by the same deflator, typically the Consumer Price Index (CPI), Wholesale Price Index (WPI), or one of their sub-indices (Source: Indian Express Explained, Sep 5, 2026). This method, however, presents a problem when the prices of inputs and outputs do not change at the same rate. If input prices rise faster than output prices, or vice-versa, single deflation can lead to an inaccurate estimation of real Gross Value Added (GVA).