In a move aimed at cooling speculative activity in India’s booming options market, the government announced an increase in the securities transaction tax (STT) on equity derivatives during the Budget presentation in Parliament on Sunday. The policy intent was clear: make high-frequency and high-risk derivative trades more expensive and discourage excessive speculation.

But the ripple effects of this decision extend beyond retail options traders. One of the most significant unintended consequences is likely to be felt in India’s arbitrage fund industry - a fast-growing category that now manages roughly $36 billion in assets.

Arbitrage funds operate on a relatively simple but highly execution-sensitive strategy. They buy stocks in the cash market and simultaneously sell futures contracts on the same stock, capturing the price differential between the two markets. These spreads are typically narrow, often in the range of 0.6% to 0.8% per month, and rely heavily on low transaction costs and efficient execution to remain viable.

The increase in STT directly raises the cost of executing this strategy because every leg of the arbitrage trade-both cash and futures-now carries a higher tax burden.

According to Aditya Agarwal, co-founder of Wealthy.in, the impact is not trivial. He estimates that the higher transaction costs could reduce annualized net returns for arbitrage funds by 25 to 35 basis points. In a category where returns are already modest and competition for spreads is intense, this magnitude of cost escalation is meaningful.

The timing is important. Arbitrage funds saw a surge in popularity over the past year as foreign portfolio investors exited Indian equities in large numbers and domestic markets delivered single-digit returns amid sluggish earnings growth and global trade tensions. Investors, seeking relatively stable, tax-efficient alternatives to equity and debt funds, moved capital into arbitrage strategies. Assets under management in the segment reportedly jumped 38% from 2024 levels.

This influx of capital was based on a key assumption: arbitrage funds offered predictable, low-volatility returns with favorable tax treatment compared to traditional debt products. The STT hike changes the math underpinning that assumption.

Harish Krishnan, Chief Investment Officer – Equities at Aditya Birla Sun Life Asset Management, which oversees nearly $22 billion in equity assets, offered a nuanced view. He noted that arbitrage is inherently dynamic. If returns fall due to higher costs, some capital is likely to exit the strategy. That reduction in participation could widen the spreads between cash and futures markets, partially offsetting the impact of higher transaction taxes.

This sets up a self-correcting mechanism. As spreads widen, the strategy becomes attractive again, but at a potentially lower equilibrium return than before.

From a market structure perspective, this development matters because arbitrage funds play a quiet but important role in maintaining price alignment between cash and futures markets. They provide liquidity, aid price discovery, and reduce inefficiencies. If participation drops meaningfully, short-term distortions between spot and futures prices could increase.

The government’s policy signal, however, is unambiguous. The focus is on reducing speculative froth in derivatives, especially in options, which have seen explosive growth in retail participation. The collateral impact on arbitrage funds appears to be an accepted trade-off in pursuit of broader market stability.

For investors, the key question now is how arbitrage funds will be positioned relative to liquid and ultra-short debt funds. If post-tax, post-cost returns narrow significantly, the tax advantage alone may not be enough to sustain the previous pace of inflows.

For asset management companies, this could mean recalibrating how arbitrage funds are marketed and setting more conservative return expectations. Portfolio managers will likely need to be more selective in trade execution, optimize turnover, and possibly reduce the scale of strategies to preserve spreads.

The immediate impact will be seen in derivatives volumes, particularly in segments where arbitrage desks are active. A temporary pullback in participation could lead to wider spreads and lower liquidity in certain contracts. Over time, a new balance is likely to emerge.