Futures Rollover: Interpreting Basis, Cost-of-Carry & Open Interest

While performing futures rollover, understanding the basis and cost of carry and their calculation is imperative. Here is a detailed breakdown:

1. Basis

The basis is simply the price difference between the current spot price of an asset and the price of its corresponding futures contract. Here is the applicable formula to calculate it:

Basis = Futures Price − Spot Price

If futures are trading higher than spot, you have a positive basis; if lower, a negative basis (less common in equity index futures). The basis captures expected costs and benefits of holding the underlying until expiry (dividends foregone, interest cost, etc.). 

For Indian index futures, this number varies across expiries and reflects the cost of carry plus market expectations. 

Suppose the NIFTY 50 is trading at ₹24,000 during an active session. Its corresponding future contract is priced at ₹24,120. Feeding this information into the above formula, we get:

Basis = ₹24,120 − ₹24,000 = ₹120

Since its future price is higher than the current spot price, it reflects a positive basis of ₹120. 

2.Cost of Carry 

Cost-of-carry measures the cost to hold the underlying asset (or maintain equivalent exposure) until the futures expiry. It includes interest cost (funding your position) less any yield/dividends you receive on the underlying, plus other costs (storage, maintenance) for physical assets. In formula form:

F = S × e^{(r + s − c) × t}

For your understanding, let us break down each of the components of this formula:

• Here, 'F' represents the futures price
• The ‘S’ represents the spot price
• ‘E’ is Euler’s number, i.e. a mathematical constant approximately 2.71828
• ‘R’ in this formula is the risk-free interest rate
• The ‘s’ represents storage and other costs
• ‘C’ means a convenience or dividend yield 
• ‘T’ is the time to expire

In equity index futures: cost of carry roughly equals (funding cost + expected dividends) over the remaining months to expiry. A high cost-of-carry means futures trade significantly above spot (wide basis). Lower cost means futures are closer to spot.

For instance, suppose the Nifty 50 is at ₹24,000 in a trading session. The annual cost of carry is at 8%. The corresponding future contract has 1 month till its expiry. The storage and other costs are 0 (since storage costs do not apply to an equity index), and the dividend yield is 2%. 

Placing this information in the above formula, we get:

F = ₹24,000 × e^[(0.08 + 0 − 0.02) × (1/12)]≈ ₹24,120

For a trader performing a futures rollover, this shows how the cost of carrying the underlying influences the futures price and, consequently, the basis.

When rolling over you are essentially paying or receiving the spread between the near-month futures and the next-month futures. That spread is a practical cost (or benefit) of staying exposed.

Key interpretations:

• Large positive basis / high roll cost: suggests higher funding cost or high dividend expectations; staying long becomes more expensive.
• Declining basis: could mean dividends expected are low, or interest rates are falling — might favour long exposure.
• Negative basis (rare in equity indices): would suggest market expects downward drift or large negative yields.

Tracking the roll cost across months gives you a sense of how much extra return you need to earn on the futures to justify holding.

Now that you know what is roll over in futures, you must understand the roles of Open Interest and the rollover percentage. These metrics help assess how actively traders are carrying their positions into the next expiry. Here is a detailed view of each of these:

1. Open Interest (OI)

Open interest (OI) is the total number of outstanding futures contracts that remain open and unsettled. Since every contract requires one buyer and one seller, 1 long position paired with 1 short position equals an OI of 1. 

It reflects how many participants are holding positions. Changes in OI along with price movement help interpret whether new money is entering the market or existing positions are being unwound.

For example, a trader sees the OI chart of a future contract rising from 80,000 to 1,00,000 contracts after a trading session. This increment of 20,000 contracts shows that future traders have opened the same number of new contracts. 

2. Rollover Percentage

This metric shows how much of the current-month contract’s open interest is carried into the next contract. For instance, suppose there are 120 lakh contracts in the August series. From those, 90 lakh contracts are being rolled over into the September series. Here, the futures rollover percentage is at 75%. 

A high rollover percentage generally suggests strong conviction among traders. It indicates a majority are choosing to maintain exposure rather than close. Conversely, a low rollover percentage may signal lack of conviction or profit-taking.

3. Interpreting OI and Rollover Data

As you may want to interpret these signals before performing a futures rollover, you must also know what each combination of price, OI, and rollover data may provide insight about market positioning. For this, take a look at the following table:

As you now have an idea about future rollovers, the basis, and cost of carry, you must also understand how Indian traders can use these metrics for futures trades. Here is a detailed breakdown:

1. Monitor Basis & Rollover Cost a Few Days before Expiry

Platforms (like 5paisa) provide data on current/next contract futures prices. Calculate the spread and compare with historical averages to judge cost. 

2. Check Futures Rollover Percentages

High rollover percentage, especially in index futures (Nifty, Bank Nifty), often signals continuation of trend. For example, a report showed a Nifty rollover of ~79% in one month. It means that traders have carried approx 79% of their open positions into the next expiry. This indicates strong position continuity.

3. Align Trade Horizon with Cost Implications

If the cost of carry is high and you have long futures anticipating a small move, the net return may flip negative after cost.

4. Use OI Movements to Validate Price Action

If price rises but OI falls sharply, the move may be fuelled by short covering, indicating less sustainability. 

5. Use Rollover Information as Sentiment Gauge

Rollover data in India is often interpreted as a bulls-vs-bears strength measure; for example, when rollover cost stays high and rollover % remains strong, bullish bias persists. 

While futures rollover may help to hold your existing position if the market is in your favour, there are still some risks that you must look out for. These generally include liquidity and slippage, unexpected events, regulatory changes, and more. For informed decision-making, factor in the following concerns:

• Liquidity & slippage in next contracts: Moving to further-out month may involve wider spreads and lower liquidity, increasing cost beyond the visible spread.
• Unexpected corporate/dividend events: For stock futures, the cost of carry may shift sharply if a large dividend is announced, affecting the basis.
• • Regulatory/contract changes: In India, exchanges may change contract specs, notional, or expiry schedule — these changes affect roll cost unpredictably.
• • Cost of carry estimates are approximate: The actual cost of carry depends on actual dividends, interest rates, and market demand — so basis alone is an indication, not an exact measure.
• • Misreading OI flows: Open interest increases can mean new longs or new shorts — context with price movement is essential; a simple rise in OI is not always bullish.