Overtrading and overconfidence

A friend asked me over the weekend why his portfolio keeps lagging the index. He watches it like a hawk. Eleven times a day, reads every print, trades on most of them. He was sure all that attention had to be worth something.

So I pulled the most famous study on the subject. Barber and Odean went through 66,465 households at a discount broker, every trade, 1991 to 1996. Then they sorted people by how much they traded.

The fifth that traded the most earned 11.4 percent a year. The market over the same stretch did 17.9. Same six years. Same stocks on the same screen. The only thing that separated them was how often they touched the portfolio.

The average household was not much better. It turned over 75 percent of its holdings every year and still finished behind the index it could have simply owned.

Here is the part nobody wants to hear. The trading itself is the cost. Every round trip pays brokerage, the securities transaction tax, the bid-ask spread, and then overconfidence steps in to pick the timing. Sell the winner, chase the noise. Run that 6.5 point yearly gap across twenty years on ten lakh and it is not a rounding error. It is most of the result.

The fix is boring, which is why it works. A rule that rebalances on a schedule trades when the weights drift, not when your hands itch. It removes the one variable the study kept punishing. You.

You do not get paid for activity in this market. You get paid for sitting still and letting the rule do the moving

The Indian version of the same study

Barber and Odean is American data from the 1990s. The fair question is whether it holds here, now. SEBI answered it twice, with the full books of the largest brokers.

The first was SEBI's study of intraday trading in the equity cash segment, published in July 2024. In FY23, 71 percent of individual intraday traders lost money after costs. Among those who made more than 500 trades in the year, it was 80 percent. The second is SEBI's study of individual traders in equity derivatives, published in August 2026: 87.7 percent of individuals lost money in FY26, down from 90.9 percent in FY25, and individuals paid about Rs 25,000 crore in transaction costs in each of those two years.

Different market, different decade, same shape. The people who touch the screen most are the ones most likely to be behind.

Costs grow faster than activity

The line in the intraday study that stayed with me is not the loss rate. It is what costs did to the people who were already losing. SEBI measured trading costs as a share of the trading loss itself. For loss makers with fewer than 10 trades a year, costs added 17 percent on top of the loss. For those above 500 trades, costs added 72 percent.

That is overconfidence with a receipt attached. Each trade feels like a small, sensible decision. The bill arrives as a sum.

One round trip, worked out in rupees

Take a delivery trade of Rs 1,00,000: you buy, and later you sell. Here is what leaves your account, using the rates in force in 2026.

• Securities transaction tax: 0.1 percent on the buy and 0.1 percent on the sell, so Rs 200.
• Stamp duty: 0.015 percent on the buy, so Rs 15.
• NSE transaction charge: Rs 3.07 per lakh on each side (rate from 1 Mar 2026), so Rs 6.14.
• SEBI turnover fee: Rs 10 per crore, so Rs 0.20.
• Brokerage: assume Rs 20 an order, so Rs 40. Your broker's rate may be lower or higher.
• GST at 18 percent on brokerage and exchange charges: about Rs 8.34.

That comes to about Rs 270, or 0.27 percent. Add the spread you cross on the way in and out. On a liquid stock, assume Rs 100 across both legs. Now one round trip costs about Rs 370, or 0.37 percent.

On its own, 0.37 percent looks harmless. What matters is how often you pay it. Turnover is the share of the portfolio you sell in a year. At 100 percent turnover you pay the round trip once on the whole portfolio. At 250 percent, two and a half times.

On Rs 10 lakh growing at an illustrative 12 percent a year for 20 years, costs alone do this:

• 25 percent turnover, roughly a once a year rebalance: about Rs 94.9 lakh.
• 75 percent, the Barber and Odean average: about Rs 91.8 lakh.
• 250 percent: about Rs 81.7 lakh.
• 500 percent: about Rs 69.1 lakh.

With no costs at all it would be about Rs 96.5 lakh. And this is only the friction. It assumes every trade was timed as well as doing nothing, which is the assumption the studies say is wrong.

The Learn module on overconfidence, anchoring and recency has a section on what it calls the screen time tax, and it is free with a quiz at the end. For the full cost stack, the trade cost calculator breaks a single order down line by line.

Why the confident trader does not see it

Overconfidence is not arrogance. It is the quiet belief that your read of today's move is better than the average read already in the price. Every single trade can be defended. The pattern only shows in a year of trades, and nobody keeps that ledger.

I see the same trap in my own work at QC Alpha. A model that rebalances every week looks smarter on paper than one that rebalances every quarter, until you price the trades. What I want from a rule is the fewest trades that still keep the portfolio where it should be. If you want to see how one bad reaction compounds, read action bias next.