Open Interest vs Volume in Options Trading: What Every Trader Should Know

What is Options Trading?

When you buy a share of a company, you own a small piece of that business. Options trading works differently. Instead of buying the share itself, you buy the right to buy or sell that share at a fixed price before a specific date. You are not obligated to go through with it; you simply have the option to do so. That is where the name comes from.

The price at which you may purchase or sell your product is known as the strike price. The period within which you need to take action is known as the expiry date. Then there is the premium that you pay for availing this privilege. It is almost similar to paying for a booking ticket. Let’s say, for example, a flat costs ₹50 lakhs and the premium you pay to book the same for 30 days is ₹50,000. In case of an increase in price, you may purchase at the previous price. If the price drops, then you may leave the deal without any further loss except ₹50,000.

Understanding Call Options And Put Options

There are two main categories of options. The first is the call option, which provides the buyer with the ability to purchase an underlying stock at a predetermined price before its expiration date. If one expects that the price of the stock will rise, he will exercise the call option. The second type of options is the put option, which entitles the buyer to sell the stock before its expiration date.

Here is a simple example. Let’s say that the stock price of a particular company is currently at ₹100. You purchase a call option for ₹110, which expires in one month’s time, for a premium of ₹5. In case the price increases to ₹130 by the time the option expires, you will make a profit of ₹20 minus premium paid. If the stock stays flat or falls, you simply let the option expire and lose only the ₹5 premium. Your downside is fixed; your potential gain is not.

Once we have the fundamentals down, the next part involves learning about volume and open interest, which tell us quite a lot about what’s going on around the options contract.

How Volume Works In Options Trading?

Volume of options refers to the total number of contracts that have been traded within a certain period of time, usually one trading day. For each transaction carried out, there is a contribution towards the daily volume. The daily volume begins from zero every day, meaning it measures only the transactions within that particular trading day.

In options, volume measures the total number of contracts trading during a session. If 20 call contracts are bought and sold in one executed trade, option volume increases by 20 contracts. If the same 20 contracts are later traded again, volume increases by another 20. If a position is closed through a separate offsetting trade, that trade also adds to volume. However, volume counts every executed trade, but it does not count the buyer and seller separately.

Simply put, options volume means how many option contracts were traded during the day. For instance, trader A buys 10 Put option contracts, the volume increases by 10. If trader A later sells those same 10 contracts to someone else, the volume increases by another 10. So, the total volume becomes 20. But here's one important thing to note: A buyer and seller are both involved in every trade, but the volume is counted only once. So, if 10 contracts are traded between a buyer and a seller, volume increases by 10 not 20.

How Open Interest Works in Options Trading?

Open interest shows how many option contracts are still open for an underlying. It rises when a new buyer and a new seller create a fresh contract. It decreases when existing positions are closed.

But if one trader simply sells an already open contract to another trade, open interest does not change. Unlike volume, open interest does not start from zero every day. As it carries forward and represents the total number of open contracts of the underlying.

 If trader A buys a 20 call option contract from trader B and both are creating a new position, open interest increases by 20.

 If trader A later sells these 20 call option contracts to trader C, and C takes over the position, open interest remains the same as earlier. However, if trader A closes the position and the other side also closes, open interest falls by 20.

Let us trace through a step-by-step example using five traders: Rohit, Priya, Arjun, Meena, and Dev.

Notice what happens in the third row. Priya sells her contract to Dev. Volume increases by 1 since a transaction is made. However, open interest remains 6 since Priya just passes on a previously held contract; nothing new has been created here. In the final row, when Rohit buys back to close his position, open interest drops because the contract is no longer active. Volume, however, keeps climbing regardless.

The principle is straightforward: Open interest will increase only when there is the creation of a wholly new contract between two parties who have not entered into any transaction before. Open interest decreases only when a contract is fully settled.

Volume VS Open Interest: The Real Difference

In reality, volume only shows activity, not whether traders are opening new positions or closing old ones. Without looking at open interest, a trader may completely misread the market.

The volume for a particular contract can be extremely large in one day since traders can constantly buy and sell contracts to each other. The open interest will remain almost static due to the fact that most of the transactions that take place are just existing contracts being sold and bought. Volume can exceed open interest, say in a case where you have a daily trading volume of 10,000 contracts while open interest remains at 5,000.

Understanding Market Behaviour Through Both Metrics

Neither number is particularly useful alone. Price shows direction, volume shows intensity, and open interest shows conviction. Here is how the combinations typically read:

By combining both indicators, traders gain a clearer understanding of whether market activity represents new speculation or simply the unwinding of older positions.

The Importance of Open Interest

In options, the sellers are typically institutional players, well-capitalised traders rather and retail participants. They write the contracts, collect the premium, and carry the obligation. High open interest typically means it is easier to trade the option because there are more market participants actively trading that contract. The increased activity leads to better liquidity, so orders fill faster with tighter bid-ask spreads.

High open interest concentrated at a particular strike price is therefore meaningful. It tells you where the more informed, better-capitalised side of the market has placed its positions. If a large number of call options show heavy open interest at a strike of ₹500 of stock, it suggests sellers expect the stock to stay below ₹500 by expiry. It is not a guarantee, but it is a useful reference point.

Options with a high number of open interest would be associated with a narrower bid/ask spread on the options premium for that particular contract, thus enabling one to get good prices. In contrast, an option with a low open interest and a low volume would feature a wider bid/ask spread, making it expensive to either buy or sell the contract quickly.

Why Volume Matters in Options Trading

Volume is your first check on whether a contract is worth trading that day. As volume increases, the bid-ask spread typically decreases, leading to more efficient pricing. A tight spread means you pay less simply to enter and exit, which directly affects your returns. 

Volume also picks up unusual activity before the broader market does. For example, if the daily average volume for a Nifty call option contract is 22,000, and suddenly its volume increases to 40,000 contracts, then either an event is anticipated or there is some information being used by the smart money. A large percentage change in the price of options combined with high volume is a good signal that the market is going in the direction of the price change.

In short, volume tells you what is happening right now. It is the most relevant number for short-term and intraday traders.

Which One is More Relevant?

Both serve different purposes and work best together. A simple way to decide which to look at first depends on what you are trying to answer:

The best way to go about this would be to look at both of them together. Traders could get valuable insights regarding the overall strength of the current market situation by examining the relationship between the two in terms of whether it’s in balance or out of balance. This tool could also come in handy for identifying trend reversals and changes in liquidity. While neither of these two variables provides a surefire prediction of the future, their combination offers a realistic overview of the current market environment.