You can check the latest margin requirements on Zerodha's margin calculator.
How F&O margin requirements work
The margin required for F&O trading changes throughout the day, and these changes are reflected in the SPAN files provided by the exchange at various times during the trading day. However, exchanges require that you maintain margins as per the beginning of the day (BOD) SPAN file.
This initial margin, as per the BOD file, is blocked for the entire day, even if the margin requirement changes due to market movements. To understand why BOD margins are considered for the entire day instead of the latest SPAN margins, visit tradingqna.com/t/peak-and-eod-upfront-margin-penalty-changes-from-may-2-2023/146585.
Why checking updated margins matters
Margins can increase drastically due to volatility, and you won't be aware of this since the margin is still blocked as per the BOD file for your positions. Zerodha updates the margin calculator to reflect the latest requirements, allowing you to check and add sufficient funds to your account.
The final SPAN file, which captures any price movements in instruments during market close, is uploaded to the margin calculator by 7:00 PM.
You should keep sufficient funds in your account above the margin requirement. A 5% buffer is sufficient on most days if there are no significant price changes. If you don't add the required margins in case of a shortfall, Zerodha may square off your position the following trading day.
The upload of intraday SPAN files to the margin calculator may vary depending on the file's availability from the exchange.