How do delta-based position limits work for index F&O trading?

If you trade index options and futures in India, SEBI sets limits on how much market exposure you can hold at any point.

The old way of measuring this, counting the number of contracts you hold, treated a deep out-of-the-money (OTM) option the same as a futures contract. That is inaccurate because an OTM option moves far less with the market than a futures contract does. Delta-based limits fix this by measuring your actual market exposure, not just your contract count.

What is delta, and how is it used in position limits?

Delta measures how much your position moves for every point move in the underlying index. A futures contract always has a delta of 1, meaning it moves in line with the index. A deep OTM Call option might have a delta of 0.20, meaning it moves only 20% as much.

The exchange doesn't count contracts directly. Instead, it calculates your Delta OI: each position weighted by its delta, added together. This shows your real directional exposure to the market.

For example, buying an OTM Put with -0.20 delta counts as only 0.20 units toward your limit, not a full unit.

What are the net delta, gross long, and gross short limits?

There are three limits to stay within. The Net Delta Limit: breaching it means you are already in violation, regardless of your gross positions. The two gross limits apply only when your net delta is within range.

• Net Delta Limit: ₹1,500 crores (EOD) / ₹5,000 crores (intraday)
  This is your total directional exposure across all Futures, Calls, and Puts combined. It cannot exceed ₹1,500 crores at end of day (EOD). During trading hours, you can go up to ₹5,000 crores, but you must bring it down by EOD. If you breach this at EOD, an Additional Surveillance Deposit (ASD) margin is blocked in your account for 30 days.
• Gross Long (Bullish) Limit: ₹10,000 crores
  This is the maximum combined exposure from Long Calls and Short Puts. You can utilise this limit only if your Net Delta is below ₹1,500 crores.
• Gross Short (Bearish) Limit: ₹10,000 crores
  This is the maximum combined exposure from Long Puts and Short Calls. You can utilise this limit only if your Net Delta is below ₹1,500 crores.
  
  Breaching either gross limit also triggers ASD for 30 days.

How is Delta OI calculated?

Zerodha calculates delta in real time using the Black-Scholes model. Here is what goes into that calculation.

Inputs

• Underlying price: Real-time value of the index at the time of each snapshot.
• Volatility: Previous day's EOD (T-1), using the higher of the index or futures annualised volatility.

Delta by contract type

The exchange defines delta (called FutEq) for each contract type:

• Call option: N(d1), a value between 0 and 1
• Put option: N(d1) - 1, a value between -1 and 0
• Futures contract: always 1

N(d1) is the cumulative normal distribution of d1, which is what the formula below produces.

The d1 formula (Black-Scholes)

d1 = [ln(S/K) + (Rf + 0.5 × Vol_Annual²) × T] / [Vol_Annual × √T]

Where:

• S = Underlying Price (real-time at snapshot)
• K = Strike Price of the option
• Rf = Risk-Free Interest Rate (latest RBI repo rate)
• AAV = Annualised applicable volatility (higher of index or futures)
• T = Pro-rated Time to Expiry (TTE), expressed as a fraction of a year

The output of d1 feeds into N(d1) to give you the delta for that option.

Time to Expiry (TTE)

TTE is expressed as a fraction of a full year (5,25,600 minutes). The minutes are counted as follows:

• Regular trading day: 12:00 AM to 12:00 AM the next day (1,440 minutes)
• Expiry day: 12:00 AM to 3:30 PM only (930 minutes)

The count starts from the time of the respective snapshot.

Example: TTE for a snapshot at 3:00:05 PM on 24th September 2025, for a contract expiring on 30th September 2025

Converting Delta OI to rupee exposure

Once delta is calculated, the exchange converts it to rupee exposure using:

OI Quantity × Delta × Underlying Price at Snapshot Time

The same real-time snapshot price used to compute delta is also used to value the position in rupees. Only the volatility input uses the previous day's EOD data.

Real example with NIFTY

NIFTY price at snapshot = 25,000

• Net Delta Exposure = 6,75,000 × 25,000 = ₹1,688 crores
• Gross Long = 14,65,000 × 25,000 = ₹3,663 crores
• Gross Short = 7,90,000 × 25,000 = ₹1,975 crores

Result: You breach the ₹1,500 crore Net Delta limit by ₹188 crores. ASD margin is blocked for 30 days. Gross limits are not breached.

What happens if I breach a limit?

The exchange provides 5 snapshot files throughout the day. Zerodha also calculates your delta exposure in real time. Once you hit the ₹5,000 crore intraday limit, the Risk Management System (RMS) may block fresh orders. You will only be allowed to reduce or exit positions.

ASD calculation:

• EOD breach: ASD = Excess Position Value - Available Cash or Equivalents (blocked for 30 days)
• Intraday breach on expiry days: ASD = (Snapshot Position Value - Limit) × 1.5

ASD applies only to intraday breaches on expiry days. Regular intraday breaches do not trigger ASD as long as you are compliant by EOD. If multiple limits are breached, only the highest excess amount triggers ASD.

Things to keep in mind

• Position tracking is dynamic. Your exposure updates with market prices. If your OTM options move ITM, their delta increases and your exposure grows, which can push you over the limit even without adding new positions.
• Limits are Permanent Account Number (PAN)-based. Multiple accounts with different PANs have separate limits. If the exchange believes you are acting in concert across PANs, it will aggregate your positions.
• Before this circular, the positional level limit stood at only ₹500 crores at Notional Value.
• The delta computation methodology follows the Standard Operating Procedure (SOP) defined by NSE for snapshot-based limit monitoring. Refer to the NSE (WEB) circular for the full details.