How to Read an Options Chain
Every column of an options chain explained — bid, ask, volume, open interest, implied volatility — using a realistic SPX 0DTE snapshot.
Once you know what a call and a put are (covered in What Is an Option?), the next step is finding a specific contract to trade. Every options platform shows a grid of available contracts — the options chain — and at first glance the columns and rows look like a wall of numbers. By the end of this article, every column should make sense.
We'll use a realistic SPX 0DTE snapshot throughout. The structure is the same on any chain you'll see.
What an options chain is
An options chain is a grid showing every option contract available for one underlying at one expiration. The typical broker layout puts calls on the left, the list of strikes down the middle, and puts on the right. Each row is one strike price; reading across that row tells you what the call and the put at that strike are priced at, plus volume, open interest, and implied volatility.
Most platforms let you toggle between expirations using a tab, dropdown, or row of dates. For an SPX 0DTE chain, you select today's expiration; that's the slice we'll work with.
A schematic of what you'll see:
| Call Bid | Call Ask | Strike | Put Bid | Put Ask |
|---|---|---|---|---|
| 21.40 | 21.60 | 4980 | 1.70 | 1.85 |
| 12.55 | 12.70 | 4990 | 2.85 | 2.95 |
| 5.85 | 5.95 | 5000 | 5.95 | 6.05 |
| 2.00 | 2.10 | 5010 | 12.45 | 12.60 |
| 0.55 | 0.65 | 5020 | 21.10 | 21.30 |
In practice each row holds more than bid and ask — usually last, mark, volume, open interest, IV, and several greeks too, all alongside the prices above. The first time you look at a chain it can feel overwhelming. The reassuring news: most of those columns mean less than you'd think, and once you know what each one is, the chain becomes scannable.
One row, decoded
Here's one row from the chain above — the 5000-strike call, expiring today, roughly four hours from the close:
| Field | Value |
|---|---|
| Bid | 5.85 |
| Ask | 5.95 |
| Volume | 7,140 |
| Open Interest | 18,300 |
| Implied Volatility | 10.2% |
Five numbers. Here's what each one means.
The price someone in the market is currently willing to pay to buy this option from you. If you wanted to sell the contract immediately, this is the price you'd get (before fees).
The price someone is willing to sell this option to you for right now. If you wanted to buy the contract immediately, this is the price you'd pay.
The gap between bid and ask. For the 5000 call above: 5.95 − 5.85 = 0.10. The spread is a real cost — if you buy at the ask and immediately sell at the bid, you lose the spread even if the market hasn't moved. Tight spreads on a liquid contract are a few cents; wide spreads on illiquid strikes can be a dollar or more.
The midpoint between bid and ask, often shown as a separate column. For the 5000 call: (5.85 + 5.95) / 2 = $5.90. The mid is the rough "fair price" used in modeling and analysis tools. It is not necessarily what you can actually transact at — your fill depends on where you place your limit order relative to the bid and ask.
The number of contracts of this exact option (this strike, this expiration, this type) that have traded today. Volume resets every morning. A high-volume strike is one the market is actively trading; low volume often means wide spreads and slow fills.
The total number of contracts of this exact option currently open — i.e. someone is long, someone is short, and the contract hasn't been closed or expired yet. OI accumulates from when the contract was first listed. Volume and OI measure different things. Volume is "how busy is this strike today"; OI is "how many positions are sitting in this strike right now."
The market's expected volatility for the underlying between now and expiration, expressed as an annualized standard deviation. The 5000 call shows 10.2% — the market is pricing in roughly that level of annualized volatility for SPX over the (very short) life of this option. IV is derived from the option's price: given the strike, expiration, and current underlying, IV is the σ that Black-Scholes would need to produce the observed market price. See Implied vs Realized Volatility for the full story.
There are usually more columns — last traded price, change since yesterday, several greeks. Each greek has its own article in the Greeks module; for now, the five above are enough to make sense of any chain.
The full chain — what shape it takes
Zoom out. Here's a fuller slice across seven strikes around the money:
Calls
| Strike | Bid | Ask | Vol | OI | IV |
|---|---|---|---|---|---|
| 4980 | 21.40 | 21.60 | 1,820 | 7,140 | 12.8% |
| 4990 | 12.55 | 12.70 | 3,250 | 9,580 | 11.4% |
| 4995 | 8.95 | 9.10 | 4,820 | 11,900 | 10.6% |
| 5000 | 5.85 | 5.95 | 7,140 | 18,300 | 10.2% |
| 5005 | 3.55 | 3.65 | 5,260 | 12,400 | 10.3% |
| 5010 | 2.00 | 2.10 | 4,850 | 10,150 | 10.5% |
| 5020 | 0.55 | 0.65 | 2,920 | 7,800 | 10.9% |
Puts
| Strike | Bid | Ask | Vol | OI | IV |
|---|---|---|---|---|---|
| 4980 | 1.70 | 1.85 | 6,840 | 18,200 | 16.1% |
| 4990 | 2.85 | 2.95 | 8,920 | 21,500 | 13.7% |
| 4995 | 4.20 | 4.30 | 9,640 | 19,800 | 12.1% |
| 5000 | 5.95 | 6.05 | 11,420 | 22,400 | 10.9% |
| 5005 | 8.55 | 8.70 | 5,920 | 14,500 | 11.6% |
| 5010 | 12.45 | 12.60 | 3,180 | 9,200 | 12.4% |
| 5020 | 21.10 | 21.30 | 1,640 | 6,100 | 14.2% |
Before walking through the patterns, three pieces of vocabulary you'll see everywhere — at-the-money, in-the-money, out-of-the-money. They describe where a strike sits relative to the current underlying price.
The strike closest to where the underlying is currently trading. With SPX at 5000, the 5000-strike row is ATM. Calls and puts at the ATM strike have zero intrinsic value and very similar premiums.
A strike where the option already has intrinsic value. A call is ITM when the underlying is above the strike (the 4980 call with SPX at 5000 is $20 in-the-money). A put is ITM when the underlying is below the strike (the 5020 put with SPX at 5000 is $20 in-the-money).
The opposite of ITM. A call is OTM when the underlying is below the strike (5020 call with SPX at 5000). A put is OTM when the underlying is above the strike (4980 put with SPX at 5000). OTM options have zero intrinsic value — their entire price is time value, covered in Intrinsic vs Extrinsic Value.
The deeper question of why ATM behaves so differently from ITM and OTM has its own article: Moneyness: ITM, ATM, OTM. For now, those three labels are enough to read what follows.
Three patterns to notice:
ATM is the most liquid strike. The 5000 strike has the highest volume and OI on both sides, and the tightest spreads (0.10 on the call, 0.10 on the put). Move a few strikes away and the picture changes. The 4980 call's spread is 0.20 — twice as wide. The 5020 call's spread is also 0.10, but on a contract priced at 0.60 that's a 17% spread.
Volume drops at the wings. Far-from-the-money contracts trade less. If you select a strike well outside ATM, expect slower fills and more give-up to the spread.
IV is not flat. Look at the IV column on the puts: 10.9% at ATM rises to 16.1% at the 4980 put. The call IV barely moves — 10.2% at ATM, 10.9% at the 5020 call. This asymmetry — OTM puts priced with substantially higher IV than OTM calls at the same distance — is the SPX volatility skew, and it's a permanent feature of index option markets. The dedicated article is The Volatility Smile and SPX Skew.
A few things specific to 0DTE chains
On a 0DTE chain, a handful of details behave differently from longer-dated chains:
Volume tells you only about today. Every option's volume counter resets each morning. On 0DTE, "today" is the entire life of the contract — so today's volume IS the contract's lifetime volume. Open interest behaves the same as on any other contract.
Quoted size shrinks near the close. ATM SPX 0DTE spreads typically stay tight throughout the day — that's what deep liquidity gives you. What changes near the close is mainly the size market makers will trade on each side: they cap their end-of-day risk, so the displayed bid/ask might still be a few cents wide but the size behind it shrinks. Larger orders may need to be broken up. Far-OTM strikes — the low-priced, high-gamma region — can see their bid-ask widen relative to the option's price as expiration approaches.
Greeks may display as zero. Some platforms round greeks to two decimals. With time-to-expiry very small, theta-per-day or vega-per-1%-vol can round to 0.00. That doesn't mean the option has no theta or vega — it means the display precision is hiding it. Tools that show per-minute or per-hour values give a more useful picture.
Far-OTM strikes can show zero volume. A 5100-strike call on a 0DTE chain with SPX at 5000 might genuinely not trade all day. Zero volume doesn't mean the contract doesn't exist; it means nobody has transacted in it yet. The quoted bid and ask are still real prices that market makers will honor (up to their quoted size).
Where to actually see one
Almost every retail broker shows an options chain. The common ones:
- Thinkorswim (Schwab) — full-featured chain with customizable columns
- Tastytrade — chain layout optimized for spread and condor selection
- Interactive Brokers — full chain with order entry inline
- Robinhood, Webull, Fidelity — simpler chain views aimed at less complex trades
Most chain views let you choose which columns to show — turn on bid, ask, volume, OI, IV, and one or two greeks; leave the rest off until you need them. Free chain viewers without an account include Cboe's own site; they're useful for browsing but you can't trade from them.
The layout — calls left, strikes middle, puts right — is standard. A few platforms flip it (puts on the left) but the columns are the same.
Key takeaways
- The bid-ask spread is a real transaction cost. Tight spreads = liquid contract; wide spreads = expensive to enter and exit.
- Volume measures today's activity. Open interest measures total open positions across the contract's life. They're different and measure different things.
- The ATM strike is the most liquid: highest volume, highest OI, tightest spreads.
- IV varies by strike, especially on SPX — OTM puts are priced with substantially higher IV than OTM calls (the volatility skew).
- On 0DTE, spreads widen sharply in the last 30 minutes. Greeks may display as zero from rounding, not because they actually are.