Lot sizes in NSE F&O contracts aren't fixed forever. They get revised periodically by the exchange, based on rules tied to contract value, and those revisions directly change how much capital and margin a single lot actually requires. Missing an update can throw off your position sizing without you realising it.
Why lot sizes change
Exchanges periodically revalue lot sizes so that the notional value of a single futures or options contract stays within a targeted range. As a stock's price moves significantly over time, its lot size may be revised up or down to keep contract value broadly consistent with exchange guidelines. This means a lot size you memorised months ago may no longer be accurate.
Why this matters for risk management
- A lot size change directly changes the capital required to take a position, and therefore your effective leverage if you're not tracking it.
- Position sizing calculations done with an outdated lot size can understate or overstate your actual risk per trade.
- Margin requirements shift alongside lot size changes, which can affect how many positions you can hold simultaneously.
Staying current
Because lot sizes are revised periodically rather than on a fixed schedule, the reliable approach is to check the current lot size directly from your broker's contract specifications or the exchange's own published data before sizing a new position — especially for stocks you don't trade often. Treating lot size as a fixed, memorised number is a small habit that can quietly throw off otherwise careful risk management.
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