Learn index vs stock futures

Overview

Index futures and stock futures are both derivative contracts that obligate the buyer to purchase (or the seller to sell) an underlying asset at a predetermined future date and price. The critical difference lies in what they track: index futures track a basket of stocks (an index), while stock futures track individual company shares.

Core Concepts

[!definition] Stock Futures

A stock future is a standardized contract to buy or sell a specific quantity of shares a single company at a predetermined price on a future date. India, one stock futures contract typically represents 1lot (lot size varies by stock, e.g., 250 shares for some, 500 for others).

Key characteristics:

• Underlying: Single stock (e.g., Reliance, TCS, HDFC Bank)
• Exposure: Company-specific risk
• Volatility: Higher (affected by company news, earnings, management changes)
• Trading: NSE/BSE during market hours
• Settlement: Cash-settled or physical delivery (in India, mostly cash)

[!definition] Index Futures

An index future is a contract based on a stock market index - a weighted average of multiple stocks. The index itself cannot be physically delivered; these are always cash-settled.

Key characteristics:

• Underlying: Market index (e.g., Nifty 50, Bank Nifty, Sensex)
• Exposure: Diversified market risk
• Volatility: Lower (smoothed across many stocks)
• Lot size: Varies (Nifty 50 = 50 units, Bank Nifty = 25 units)
• Settlement: Always cash-settled

[!intuition] Why Two Types Exist

Think of it like this: stock futures let you bet on whether Apple will outperform the market, while index futures let you bet on whether the entire tech sector (or whole market) will rise or fall.

WHY would you choose one over the other?

1. Diversification needs: Index futures give instant diversification. If you think "the market will rally" but don't know which specific stocks, buy Nifty futures. If you believe "Reliance will beat the market", buy Reliance futures.

2. Risk appetite: Stock futures have idiosyncratic risk (company-specific events like CEO resignation, earnings miss). Index futures have only systematic risk (overall market movements).

3. Capital efficiency: Index futures often require lower margins relative to the exposure they provide, since the index's volatility is lower than individual stocks.

4. Hedging strategy:

   • Portfolio manager holding30 stocks → hedge with index futures (simpler than 30 individual hedges)
   • Investor holding only Infosys → hedge with Infosys stock futures (precise hedge)

Detailed Comparison

| Aspect | Stock Futures | Index Futures | |--------|---------------| | Underlying Asset | Single company stock | Basket of stocks (index) | | Contract Value | Lot size × stock price | Lot size × index level | | Margin Required | Higher (15-40% typically) | Lower (10-15% typically) | | Price Driver | Company fundamentals + market sentiment | Overall market sentiment + economic indicators | | Liquidity | Varies (high for large-caps, low for small-caps) | Very high (Nifty, Bank Nifty) | | Expiry Impact | Moderate volatility | High volatility on expiry day | | Use Case | Directional bet on specific stock, arbitrage | Market hedging, portfolio replication, macro bets |

[!formula] Contract Value Calculation

For Stock Futures: $\text{Contract Value} = \text{Lot Size} \times \text{Futures Price}$

WHY this formula? The lot size is fixed by the exchange (standardization requirement). The futures price is determined by the no-arbitrage condition (cost-of-carry model). Multiplying gives you the total notional exposure.

Example: Reliance futures with lot size 250, trading at ₹2,500 $\text{Contract Value} = 250 \times 2500 = ₹6,25,000$

For Index Futures: $\text{Contract Value} = \text{Lot Size} \times \text{Index Level}$

HOW does this work? The index level (e.g., Nifty at 18,500) is not a "price" but a weighted average. The exchange assigns a lot size (for Nifty, it's 50) to convert this dimensionless number into a tradeable contract.

Example: Nifty 50 at 18,500 with lot size 50 $\text{Contract Value} = 50 \times 18500 = ₹9,25,000$

[!formula] Margin Requirements

The exchange determines margins using SPAN (Standard Portfolio Analysis of Risk) margins. The formula is complex, but the principle:

$\text{Margin} = \text{VaR}(\text{portfolio}, 99\%, 1\text{-day}) + \text{ELM}$

Where:

• VaR = Value at Risk (worst expected loss in 1 day with 99% confidence)
• ELM = Extreme Loss Margin (tail risk buffer)

WHY is index margin lower? Diversification! The index's daily volatility is lower because individual stock movements partially cancel out.

Typical margins (rule of thumb):

• Nifty futures: 10-12% of contract value
• Stock futures: 15-40% (higher for volatile stocks)

[!example] Worked Example 1: Hedging with Index Futures

Scenario: You manage a ₹50 lakh portfolio that closely tracks the Nifty 50. You fear a market correction over the next month but don't want to sell your holdings (tax implications, transaction costs).

Step 1: Calculate hedge ratio $\text{Number of contracts} = \frac{\text{Portfolio Value}}{\text{Contract Value}} = \frac{50,00,000}{50 \times 18,500} = \frac{50,00,000}{9,25,000} \approx 5.4$

Why this step? You need enough futures contracts so that if the index falls 1%, your futures gain offsets your portfolio's 1% loss.

Step 2: Round and execute Short 5 Nifty futures contracts (round down for conservative hedge).

Step 3: Outcome analysis

• If Nifty falls 5% to 17,575:
  • Portfolio loss: ₹50L × 5% = ₹2,50,000
  • Futures gain: 5 contracts × 50 × (18,500 - 17,575) = 5 × 50 × 925 = ₹2,31,250
  • Net loss: ₹18,750 (imperfect hedge due to rounding and tracking error)

Why does this work? Index futures move nearly1:1 with your portfolio (assuming high correlation), so shorting them creates an offseting position.

[!example] Worked Example 2: Speculating with Stock Futures

Scenario: You believe Tata Motors will announce strong EV sales next week. Current price₹650, futures₹655 (lot size 1,500).

Step 1: Calculate investment Margin required (assume 20%): ₹655 × 1,500 × 0.20 = ₹1,96,500

Why this step? You don't pay the full contract value (₹9,82,500), only the margin. This is leverage.

Step 2: Buy 1 lot You buy 1 Tata Motors futures contract at ₹655.

Step 3: Outcome (price rises to ₹700)

• Profit: (₹700 - ₹655) × 1,500 = ₹67,500
• Return on margin: ₹67,500 / ₹1,96,500 = 34.35%
• Actual stock movement: (₹700 - ₹650) / ₹650 = 7.69%

Why the difference? Leverage! You controlled ₹9.8L worth of stock with ₹1.96L.

Step 4: Outcome (price falls to ₹630)

• Loss: (₹630 - ₹655) × 1,500 = -₹37,500
• Return on margin: -19.1%

Risk: If losses exceed your margin, you get a margin call - you must add funds or the position is liquidated.

[!example] Worked Example 3: Arbitrage Opportunity

Scenario: Nifty spot at18,500, Nifty futures (1-month) at 18,650. Risk-free rate 6% p.a., no dividends expected.

Step 1: Calculate fair value Using cost-of-carry: $F = S \times e^{r \times t} = 18,500 \times e^{0.06 \times \frac{1}{12}} = 18,500 \times e^{0.005} = 18,500 \times 1.00501 = 18,592.69$

Why this step? In a no-arbitrage market, futures should trade at the spot price plus the cost of carrying the position (interest cost).

Step 2: Identify mispricing Futures at 18,650 > Fair value18,592.69 → Futures overpriced by ₹57.31

Step 3: Execute arbitrage (Cash-and-Carry)

• Borrow ₹9,25,000 at 6% for 1 month
• Buy Nifty portfolio (replicate index) at 18,500
• Sell Nifty futures at 18,650
• Hold until expiry

Why this works? At expiry, futures converge to spot. You:

1. Repay loan + interest: ₹9,25,000 × (1 + 0.06/12) = ₹9,29,625
2. Sell portfolio at spot (= futures settlement): 18,650 × 50 = ₹9,32,500
3. Profit: ₹9,32,500 - ₹9,29,625 = ₹2,875 risk-free

Real-world note: Transaction costs and tracking error usually eliminate such mispricings quickly.

Common Mistakes

[!mistake] Mistake 1: Using Index Futures to Hedge Individual Stocks

Wrong approach: Holding only Infosys, hedge by shorting Nifty futures.

Why it feels right: "Infosys is in the Nifty, so if Nifty falls, Infosys will fall too."

The steel-man argument: This isn't completely wrong - Infosys has a beta to the Nifty (systematic risk component). If the whole market crashes, Infosys likely falls.

Why it's still wrong: Infosys has a Nifty weight of only ~3-4%. Its movements are dominated by company-specific factors (earnings, atrition, deal wins). The hedge ratio would be:

$\text{Hedge contracts} = \frac{\text{Infosys Value}}{\text{Nifty Contract}} \times \beta_{\text{Infosys}}$

Even with perfect beta estimation, you're hedging systematic risk only. If Infosys-specific bad news hits (CEO resigns, contract loss), you lose on the stock AND on the short futures position if the market rallies.

The fix: Use Infosys stock futures for precise hedging. Use index futures only for portfolio-level systematic risk.

[!mistake] Mistake 2: Ignoring Basis Risk in Index Futures

Wrong assumption: "My portfolio tracks Nifty, so shorting Nifty futures is a perfect hedge."

Why it feels right: The math (hedge ratio calculation) seems airtight.

The steel-man: If your portfolio IS the Nifty (same weights, same stocks), this works perfectly.

Why it fails: Most portfolios deviate from the index:

• Different weights (overweight in some sectors)
• Missing stocks (holding30 stocks vs. Nifty's 50)
• Tracking error accumulates over time

Example: Your portfolio has 30% IT stocks vs. Nifty's 15%. If IT rallies but broader market falls, your portfolio might rise while Nifty falls. Your short Nifty futures lose money while your portfolio gains less than expected - double whammy.

The fix: Calculate your portfolio's beta to the Nifty using regression: $R_{\text{portfolio}} = \alpha + \beta \times R_{\text{Nifty}} + \epsilon$

Adjust hedge ratio by beta: $\text{Contracts} = \frac{\text{Portfolio Value}}{\text{Contract Value}} \times \beta$

[!mistake] Mistake 3: Confusing Lot Size with Share Quantity

Wrong calculation: "Nifty at 18,500, I want₹10L exposure, so I need ₹10L / ₹18,500 = 54 contracts."

Why it feels right: You're dividing money by price, like buying stocks.

Why it's wrong: You forgot the lot size! Each Nifty contract = 50 units.

Correct calculation: $\text{Contract Value} = 50 \times 18,500 = ₹9,25,000$ $\text{Contracts needed} = \frac{10,000}{9,25,000} = 1.08 \approx 1$

The fix: Always calculate: Number of Contracts = Desired Exposure / (Lot Size × Futures Price)

Strategic Use Cases

When to Use Stock Futures:

1. Concentrated bet: High conviction on a specific company's earnings, product launch, merger
2. Event-driven trading: FDA approval, election impact on specific sector stock
3. Pair trading: Long Stock A futures, Short Stock B futures (both in same sector, different fundamentals)
4. Covered calls on steroids: Use futures for leverage while keeping cash for other opportunities

When to Use Index Futures:

1. Market timing: Bullish/bearish on overall economy, interest rates, GDP growth
2. Portfolio hedging: Protect diversified holdings from market crashes
3. Asset allocation shifts: Quickly gain/reduce equity exposure without stock transactions
4. Arbitrage: Exploit mispricing between spot index and futures
5. Overnight exposure: Use futures to get market exposure when equity markets are closed (limited hours for futures)

Key Relationships

[!formula] Beta Relationship (Stock to Index)

$\beta_{\text{stock}} = \frac{\text{Cov}(\text{R}_{\text{stock}}, \text{R}_{\text{index}})}{\text{Var}(\text{R}_{\text{index}})}$

WHY this matters: Beta tells you how many index futures contracts hedge one stock futures contract.

Derivation from first principles:

Start with the stock return decomposition: $R_{\text{stock}} = \alpha + \beta R_{\text{index}} + \epsilon$

where $\epsilon$ is idiosyncratic risk (mean zero, uncorrelated with index).

To find $\beta$, take covariance of both sides with $R_{\text{index}}$: $\text{Cov}(R_{\text{stock}}, R_{\text{index}}) = \beta \cdot \text{Cov}(R_{\text{index}}, R_{\text{index}}) + \text{Cov}(\epsilon, R_{\text{index}})$

Since $\epsilon$ is uncorrelated with index: $\text{Cov}(\epsilon, R_{\text{index}}) = 0$

And $\text{Cov}(R_{\text{index}}, R_{\text{index}}) = \text{Var}(R_{\text{index}})$

Therefore: $\beta = \frac{\text{Cov}(R_{\text{stock}}, R_{\text{index}})}{\text{Var}(R_{\text{index}})}$

Example: If Reliance has $\beta = 1.2$ to Nifty:

• Nifty up 1% → Reliance expected to rise 1.2%
• To hedge 1 lot Reliance futures, short $1.2 \times \frac{\text{Reliance contract value}}{\text{Nifty contract value}}$ Nifty futures

[!formula] Index as Weighted Average

For an index with $n$ stocks: $I_t = \frac{\sum_{i=1}^{n} w_i \cdot P_{i,t}}{\text{Divisor}}$

WHY the divisor? Historical reasons - when a stock splits or is replaced, the divisor adjusts so the index doesn't jump artificially.

WHAT are the weights?

• Free-float market cap weighted (Nifty, Sensex): $w_i = \frac{\text{Market Cap}_i}{\sum \text{Market Cap}_j}$
• Price-weighted (Dow Jones): Each stock's price contributes equally per share

HOW does this affect futures? A large-cap stock (high weight) moving 1% has more impact on index futures than a small-cap moving 5%.

Connections

• Cost-of-Carry Model - Pricing relationship between spot and futures
• Margin Requirements SPAN - Risk-based margining system
• Beta and Systematic Risk - How stocks correlate with market indices
• Calendar Spreads - Trading near vs. far month futures
• Arbitrage Strategies - Exploiting index vs. stock mispricing
• Portfolio Hedging Techniques - Using derivatives for risk management
• Liquidity and Impact Cost - Why index futures trade more volume
• Options vs Futures - Alternative derivative instruments

[!mnemonic] Remember the Key Difference

"S.I.D - E.V.E."

• Stock futures: Single company

• Index futures: Index basket

• Diversification: Different risk profiles

• Exposure: Equity market (index) vs. entity-specific (stock)

• Volatility: Varied (stock > index)

• Efficiency: Easier hedging with index for portfolios

[!recall]- Explain This to a 12-Year-Old

Imagine you and your friends collect trading cards.

Stock futures are like making a deal with your friend: "In one month, I'll buy your rare Pokémon card for $50, no matter what price it is then." You're betting that one specific card will be worth more than$50 by then. If that card's price drops because the player gets injured or the card gets reprinted, you still have to pay $50 - ouch!

Index futures are like making a deal for an entire starter deck (30 cards). You're betting that the average value of all those cards will go up. Maybe one card crashes, but if most cards do well, you're safe. It's like betting on the whole class doing well on a test instead of betting on just one student.

Why would you pick one over the other?

• If you really believe that one specific Pokémon (like Charizard) will become super popular because of a new movie, bet on that one card (stock futures).
• If you just think "trading cards are getting popular in general" but don't know which specific one, bet on the whole deck (index futures).

The cool part? You don't need to pay the full $50 now - you just keep a "safety deposit" (margin) of maybe$10. If you're right and the card/deck goes to $60, you make$10 profit on just a $10 deposit - you doubled your money! But if you're wrong and it drops to$40, you lose that $10 deposit and might even owe more.

Practice Questions

#flashcards/stock-market

What is the key difference between stock futures and index futures? :: Stock futures track a single company's shares, while index futures track a basket of stocks (market index). Stock futures have higher volatility and company-specific risk; index futures have lower volatility with diversified market risk.

Concept Map

Hinglish (regional understanding)