A Benchmark Index is a standard against which the performance of a portfolio, mutual fund, or investment strategy is measured. In India, the Nifty 50 and the S&P BSE Sensex are the most widely used benchmark indices for large-cap equity funds, while the Nifty Midcap 150 and Nifty Smallcap 250 serve as benchmarks for mid and small-cap funds respectively. SEBI mandates that all mutual funds disclose their designated benchmark index to enable transparent performance comparison for investors.