An options chain is the menu of every option contract available on a stock, laid out by expiry date and strike price, with calls on the left and puts on the right. Reading it means decoding a handful of columns – bid, ask, volume, open interest and implied volatility – to judge what a contract really costs and whether it is liquid enough to trade.

A chain looks intimidating – a wall of numbers in tiny type – but it is built from a few repeating ideas. Once you can read those, you can size up any contract in seconds. This guide walks each column in plain English, with a worked chain throughout.

The anatomy of a chain – calls, puts and strikes

An options chain is organised first by expiry date, then by strike price. For a single expiry you read it as three columns: calls on the left, the strike prices down the centre, and puts on the right. Each row is one strike, and the same strike gives you both a call and a put.

Throughout this guide we use a fictional London-listed stock, HLXB.L, trading at 100p, with strikes running from 90p to 110p. The strike nearest the current price – here the 100p row – is the at-the-money (ATM) strike, and it is the busiest part of any chain.

Bid and ask – the two prices that matter most

Every contract shows two live prices. The bid is the highest price a buyer will pay right now – it is what you receive if you sell immediately. The ask (or offer) is the lowest price a seller will accept – it is what you pay if you buy immediately. The midpoint sits halfway between and is a fair reference for the contract’s true value.

If you bought this call and immediately changed your mind, you would buy at the 4.4p ask and sell back at the 4.0p bid – down 0.4p before the stock moves at all. That gap is the cost of doing business, and it is the next thing to understand.

The bid-ask spread – your hidden cost

The bid-ask spread is the difference between the ask and the bid, and it is the single best gauge of how cheap a contract is to trade. It matters because you pay it twice – once on the way in and again on the way out. The useful number is the spread as a percentage of the ask:

• Below 10% – excellent. A liquid, efficient contract.
• 10% to 20% – acceptable, but check open interest before committing.
• Above 20% – caution. The spread alone is eating a large slice of any gain.

Take the 105p call: a 1.9p bid and a 2.3p ask is a 0.4p spread, which is 0.4 ÷ 2.3 = 17% of the ask. Borderline – tradable, but worth checking liquidity first. Compare that with a thinly-traded strike on a 36% spread: for every £100 of premium, £36 goes on spread friction on entry alone, and again on exit. Even a correct call on direction can lose money there.

Volume and open interest – reading liquidity

Two columns measure how actively a contract trades, and they are easy to confuse. Volume is the number of contracts traded so far today, and it resets to zero every session. Open interest (OI) is the total number of contracts currently outstanding – positions opened and not yet closed – and it builds up over time across many sessions.

Open interest is the more reliable liquidity signal because it reflects standing commitment, not just one busy morning. Here is the call side of our chain:

The 100p ATM strike has the deepest open interest at 3,890 – typical, because at-the-money options attract both hedgers and speculators. As a rule of thumb, treat OI of at least 500 as the floor for a contract you intend to trade actively; below about 100 and you may struggle to get a fair fill at all.

Implied volatility – the price of uncertainty

Implied volatility (IV) is the market’s forecast of how much the stock will move, expressed as an annualised percentage. It is the single biggest driver of an option’s time value: higher IV means a fatter premium, because a bigger expected swing makes the option more likely to pay off.

The catch is that you can be right on direction and still lose. After a scheduled event – earnings, a regulatory decision – the uncertainty resolves and IV can collapse in an instant. This is IV crush: the stock moves your way, but the premium deflates faster than the move adds value, and the position falls.

The volatility smile – why far options can cost more

Look down the IV column and you will notice it is not flat. The ATM 100p call sits at 27%, but the out-of-the-money 110p call is up at 32%, and the deeper strikes lift again. Plotted across strikes, IV forms a curve – the volatility smile (or, when lopsided, a skew).

The driver is demand. Cheap, far-out-of-the-money calls are popular lottery tickets: low cost, large payoff if the stock surges. That steady speculative demand inflates their implied volatility. Counter-intuitively, the 110p call is less likely to finish in-the-money than the 100p ATM call, yet it carries a richer IV – because people keep buying the long shot.

IV rank – are options cheap or expensive right now?

A single IV figure tells you little on its own; 27% might be high for one stock and low for another. IV rank (IVR) fixes that by placing the current IV against its own 52-week range, on a 0 to 100 scale:

The broad logic: high IV rank favours strategies that sell premium; low IV rank favours strategies that buy it. You are judging whether the option is expensive or cheap relative to its normal, not in absolute terms.

Choosing your expiry – days to expiry

Days to expiry (DTE) is the calendar time left on the contract, and it governs how much time value you are paying for. Too little and decay works against you brutally; too much and you over-pay for time you may not need. For most directional trades, a 30 to 60 day window is the practical sweet spot.

One rule overrides the rest: always choose an expiry that falls after any event you are trading. An option that expires the week before earnings captures none of the move you are betting on – the catalyst arrives after your contract is already dead.

Picking a contract – a liquidity checklist

Put the columns together and contract selection becomes a quick screen rather than a guess. Before committing to any option, run it past these checks:

• Open interest of 500 or more – enough standing liquidity to enter and exit fairly.
• Spread under 10% of the ask – so friction is not quietly taxing the trade.
• 30 to 60 days to expiry – and always past your catalyst date.
• Use a limit order, never a market order – on a wide options spread a market order can fill far from the midpoint. A limit at or near the ask controls your entry.

Applied to four candidate calls, the screen is decisive:

The 100p ATM call wins on all three counts – deepest liquidity, tightest spread, and a DTE in the optimal window. One last note on size: UK-listed equity options typically represent 1,000 shares per contract, where the US standard is 100 – so always confirm the contract multiplier before you calculate what a position actually costs.