The STT on an option sale rose from 0.05% to 0.15% of premium, so a dated backtest needs each date's rate
A backtest tests the rules on past prices. An account pays costs on every trade: STT, exchange transaction charges, stamp duty, GST on brokerage, and the slippage between the price a rule expects and the price it gets. Leave any of these out and the test measures a gross result that no account can keep.
STT is one of the statutory items, and its rates have changed in steps. The chart lists the rates that applied from each date. Since 1 Apr 2026 the sale of an option carries 0.15% of premium, and an option that is exercised is charged on its intrinsic value. Before that date the earlier rates in the chart applied, so a trade from one year and a trade from another do not cost the same.
Build the cost into each trade on the date it happened. A flat cost taken from the latest rate hides the change and flatters older years. Keep the costs in a separate table, so each rate can be checked against the NSE circular that set it and a reader can see how much of the result the costs take. The STT question sets out the rates in full.
Costs are not the whole test. Slippage depends on the book, the size and the time of entry, so a backtest that fills at the close needs a stated slippage rule. A result that stays positive after dated, costed and slipped trades is still a test on past data, and an out of sample check has to confirm it.
Before you trade. Derivatives trading carries a high risk of loss. SEBI's study "Profitability of Individual Traders in the Equity Derivatives Segment (FY25 to FY26)" (August 2026) found that 87.7% of individual traders in equity F&O made net losses in FY26, with aggregate net losses of Rs 91,685 crore. Read the SEBI study