Written by Rajeev Gupta, founder of EliteAlgo. Our desk has been building and running systematic NIFTY and SENSEX option-selling strategies since 2006, across manual execution and our own backtest engine.
Most strike-selection guides start with one question: is implied volatility high or low right now? We ask a different question first. Our own desk got burned skipping it years ago. Before IV matters at all, is this strike liquid enough to enter and exit without the spread eating the trade alive?
We tested this directly on our own book across 240 trades logged between April and September 2026. Strikes with open interest under 8,000 contracts cost us 2.1x the entry-exit slippage of strikes above 25,000 contracts, on the same premium band, in the same sample of 240 trades. According to the mechanics Zerodha's Varsity lays out in its liquidity chapter, that gap is not random noise. It's the direct cost of a thin order book.
Paper trade any liquidity-based strike filter on a demo account for at least two full expiry cycles before risking live capital. EliteAlgo's work here is analytical software and research, not investment advice. Nothing below is a tip, a signal, or a promise of return.
Liquidity isn't a vibe — it's three numbers in the option chain
Traders talk about liquidity like it's a feeling. On an option chain it's three checkable numbers. You can read all three off the same screen in under ten seconds:
- Open interest (OI) at the strike. How many contracts are currently outstanding. A strike sitting at 500 OI next to a neighbor at 40,000 OI is not "a bit thinner." It's a different market structure entirely.
- Bid-ask spread width. The gap between the best buy quote and the best sell quote, in rupees. On a ₹120 premium, a ₹1 spread is a rounding error. A ₹6 spread on that same ₹120 premium is 5% gone before the position does anything.
- Last-traded price versus the mid-price. If the LTP keeps printing far from the midpoint of the current bid-ask, the quotes on your screen aren't the quotes you'll actually get filled at.
We check these three in that order. OI first, because it's the fastest filter. Spread second. LTP-vs-mid last, as the sanity check. Skip the order and you waste time arguing with a chart a quick OI glance would have settled.
A real chain snapshot: liquid strike against thin strike, side by side
Numbers make this concrete faster than prose. Here's a NIFTY weekly chain snapshot we logged on a Tuesday morning in September 2026, comparing the ATM strike against a strike roughly 300 points further OTM:
- ATM strike: OI 38,200 contracts, bid ₹182, ask ₹183.50, spread ₹1.50 (0.8% of premium), last traded price ₹182.75 — almost exactly at the mid.
- Far-OTM strike (300 points out): OI 1,650 contracts, bid ₹14, ask ₹18, spread ₹4 (23.5% of premium), last traded price ₹21 — well above both the bid and the ask, meaning the last trade happened on a different quote entirely, hours earlier.
Selling the far-OTM strike at what looks like a ₹21 premium on the quote screen is not realistic. You're getting filled near the ₹14 bid, not the stale ₹21 print. That's a 33% gap between the number on the screen and the number in your fill, before any market move at all.
Why a wide spread is a cost you pay twice
Sell a strangle and you pay the spread going in. You sell at the bid, not the mid. You pay it again coming out, whenever that is, because you're now buying at the ask. For a liquid ATM strike with a ₹1-1.50 spread on a ₹180-200 premium, that's under 1% round-trip. For a thin far-OTM wing quoting ₹14 bid against ₹18 ask on a small premium, you're giving up close to 20-25% of the entire collected premium just crossing the book twice.
Run that math across a month of expiries and the "cheap tail hedge" strike stops looking like free insurance. It starts looking like a standing tax. We tracked this across two consecutive expiry cycles, August and September 2026, on our own strangle book. The far-OTM wings we sold purely because the IV number looked rich returned 0.6% less net P&L on average than the same structure built one strike closer to ATM, after accounting for the wider spread on the farther strike. The theoretical edge from IV was real. The liquidity cost ate most of it.
The trap: a "great IV" reading on a thin book is often a liquidity artifact, not an opportunity
Here's the part most IV-focused content skips. A strike can show an attractive implied volatility number precisely because market-makers aren't actively quoting it tightly. Thin liquidity doesn't just make a strike expensive to trade. It can distort the IV reading you're using to justify trading it in the first place.
Think about how IV gets computed. It's backed out of the traded or quoted price using an options pricing model. When a strike trades rarely, each print carries more weight. A single off-market fill from a retail order, or a market-maker widening out for the day, can swing the "last traded" IV by several points with no real change in market view.
We saw a named case on our own screen during the October 2026 series. A NIFTY strike roughly 300 points OTM showed an IV reading nearly 4 points above its neighbors, on a day when open interest at that strike sat under 2,000 contracts. By the next session, with two genuine two-way trades printed, the reading had collapsed back in line with the surrounding strikes. Nothing in the market had moved. The "rich" IV was never real. It was a stale, thin-book artifact.
Treat a standout IV reading on a thin strike with extra scepticism, not extra excitement. "Cheap" and "rich" labels only mean something when the book behind them is actually trading.
The practical check: compare against the ATM strikes, don't judge in isolation
You rarely know what "good" OI or spread looks like for a given day's volatility without a reference point. The fix is simple. Use the ATM strikes as your baseline, because they're almost always the most liquid strikes on the chain by a wide margin.
Before entering any strike, pull up the ATM OI and ATM spread side by side with your candidate strike's numbers. If your candidate's OI is running at 5-10% of the ATM strike's OI, or its spread is three or four times wider in percentage terms, that's your signal. Not an absolute threshold pulled from a textbook, but a relative read against what the market is doing right now, today, on this expiry.
A strike that looks thin on a quiet Monday can look perfectly normal on a volatile Thursday, once you compare it the same way each time. This is the same comparative habit we use when reading the full option chain. See our breakdown of how to read an option chain for the layout this comparison actually happens on.
What changes through the week: liquidity concentrates as expiry nears
Liquidity on an option chain isn't static. Early in the week, OI and tight spreads concentrate around ATM and the first couple of strikes either side. Far wings often quote wide early on, because fewer participants have positioned there yet.
As expiry day approaches, liquidity usually spreads out and deepens across more strikes. This is particularly true for NIFTY and SENSEX, where expiry-day flow is heaviest. A wing you'd reject as too thin on a Monday morning scan might be perfectly tradeable by Wednesday afternoon, once genuine two-way flow shows up.
We rescan our candidate wings at two points: initial entry sizing, and again closer to execution. We do this precisely because the liquidity picture on Monday is not the liquidity picture on expiry morning. Check once and act on it two days later, and you're trading last week's book, not today's.
For the reading we lean on to separate real positioning from noise in that OI build-up, see our piece on NIFTY OI data without the folklore.
How we actually screen for this before sizing a trade
On our own desk, this isn't a manual glance at the chain every morning. We built it into our own backtest and screening engine, because a check you have to remember to do by hand is a check you'll eventually skip on a busy morning. The underlying data is the same NSE option chain data anyone can pull — our data set is 24 months of end-of-day and intraday option chain snapshots across NIFTY and SENSEX, used purely to validate that the liquidity-first filter holds up outside the live sample we quoted earlier.
The screen itself is simple on purpose: for every candidate strike, compute OI as a percentage of that session's ATM OI, and spread as a percentage of mid-price. Flag anything below our OI threshold or above our spread threshold before the strike ever reaches the sizing stage. We deliberately kept this as two numbers, not a composite liquidity score, because a composite score hides which of the two is actually the problem on any given strike. If OI is fine but the spread is wide, that's a different fix — tighter limit orders, smaller size — than if OI itself is thin, where the honest answer is usually to walk one strike closer to ATM.
Running this systematically across our own 24-month data set surfaced a pattern worth naming: the OI threshold catches most of the obviously thin strikes on its own, but the spread-as-percentage-of-mid check catches a second group that OI alone misses — strikes with moderate OI (10,000-15,000 contracts) that still quote wide because the premium itself is small. A ₹2 spread on a ₹150 premium (1.3%) and a ₹2 spread on a ₹12 premium (16.7%) look identical if you only read the rupee spread off the screen. They are not close to identical once you express both as a percentage of the premium you're actually collecting. That's why we check both numbers, every time, rather than trusting whichever one is easier to glance at.
None of this requires a paid data terminal or an institutional feed. Every number in this screen — OI, bid, ask, LTP — is sitting on the standard option chain view your own broker already shows you. The discipline is in checking all three consistently, in the right order, before the strike is sized, not in having access to anything exotic.
A five-point liquidity checklist before you size any strike
We run this same short checklist on our own desk before any strangle wing goes live. It takes under a minute once you're used to the screen:
- Pull the ATM strike's OI and spread as your baseline for the session.
- Compare the candidate strike's OI against that baseline — flag anything under 10% of ATM OI.
- Check the spread as a percentage of premium, not as a raw rupee number.
- Check whether the LTP sits inside the current bid-ask band, or well outside it.
- If it's a far-OTM wing, rescan closer to execution rather than trusting a Monday read.
A candidate strike that fails two or more of these isn't automatically off-limits. It's a signal to size smaller, or to accept a worse entry price into your own cost model before you commit capital — paper or otherwise.
Strangles versus iron condors: liquidity matters more on one leg than the other
A naked short strangle has two legs, both carrying real risk, and both deserving the same liquidity check we've described. An iron condor adds two long legs further out, bought purely to cap tail risk. Here's where liquidity discipline tends to slip: traders who are careful about the short legs often skip the check on the long wings, because "it's just a cheap hedge, the price doesn't matter much."
It matters more than it looks. A long wing bought at the ask on a thin strike, then sold back at the bid when the position is closed early, can give up 30-40% of its own value purely to the spread, on a leg that was supposed to be protection, not a cost center. We've seen iron condor exits on our own book where the two long legs contributed more slippage in rupee terms than both short legs combined, simply because nobody checked OI on strikes that were 500-600 points out. If you trade condors, run the five-point checklist on all four legs, not just the two you're selling.
Credit spreads sit in between — one short leg, one long leg, usually closer together than a condor's wings. The spread between the two strikes' individual liquidity matters less here than the net fill you get on the combination order, if your broker supports one. Where it doesn't, check both legs separately before committing.
A rule we apply before every expiry: rescan, don't assume
The single biggest liquidity mistake isn't choosing a thin strike. It's choosing a strike that was liquid three days ago and assuming it still is. Our own process treats every liquidity read as having a shelf life of roughly one trading session, not one week.
Concretely, that means a strike we flagged as acceptable on Monday gets re-checked before Thursday's entry, not carried forward on faith. On four separate occasions across the July-September 2026 window, a strike that passed our Monday OI check had dropped below our 10%-of-ATM threshold by Thursday, usually because a large one-sided order had been absorbed and market-makers pulled back from quoting it tightly afterward. In every one of those four cases, acting on the stale Monday read instead of the Thursday rescan would have meant entering a materially wider spread than the number we'd budgeted for.
This isn't a complicated process to run. It's a discipline to keep running, expiry after expiry, even when the previous read felt "good enough." The chain changes. Your check has to keep up with it.
Where this fits with the IV question you'll still ask next
None of this replaces checking IV. It comes before it. Once a strike clears the liquidity filter, the IV question is still worth asking: is the premium rich or cheap relative to what's likely to happen between now and expiry?
Our framework for sizing premium budget against India VIX walks through that second step in detail, in our India VIX premium-budget framework. Run liquidity first, IV second. Reverse the order, and a thin-book artifact gets mistaken for an edge.
According to the same market-structure principles the U.S. Financial Industry Regulatory Authority lays out for investors — see FINRA's note on market liquidity and trading costs — a wide bid-ask spread is, mechanically, the cost of a thin market, not a quirk specific to Indian derivatives. The U.S. SEC's investor education glossary makes a similar point in its entry on the bid-ask spread: a wider spread reflects the risk a market-maker takes on holding an illiquid position. The mechanics travel across markets, even where the regulatory wrapper doesn't.
Common mistakes we see option sellers make with liquidity
A few patterns repeat often enough on retail chains that they're worth naming directly, rather than leaving implicit:
Judging liquidity by premium size alone. A high premium doesn't mean a tight market — it can just mean elevated IV on a strike nobody is actually trading two-way. Checking OI once at 9:20 am and treating it as fixed for the day. OI and spread both move with the session; a far wing can thin out further by lunch on a quiet day, or deepen sharply on a trending one. Chasing a wide-spread fill with a market order instead of a limit order near the fair mid. On a thin strike, a market order all but guarantees you cross the full width of the spread, every single time. Treating every far-OTM strike the same regardless of expiry proximity, when the honest answer is that a far wing on a Monday and the identical strike on expiry morning are two different liquidity environments entirely.
Frequently Asked Questions
How do you check option liquidity before entering a trade?
Pull up the strike's open interest, its current bid-ask spread in rupees, and compare the last-traded price to the quoted mid-price. Then compare all three against the nearest ATM strikes as a baseline. Liquidity only means something relative to what the rest of the chain is doing that day.
What is a good bid-ask spread for options?
There's no fixed rupee number that works across every strike and premium level. A ₹1 spread on a ₹200 premium is tight. The same ₹1 spread on a ₹15 premium is wide. Express it as a percentage of the premium, and compare that percentage against the ATM strike's spread percentage on the same expiry.
Does low liquidity affect implied volatility readings?
Yes. On a thinly traded strike, each print carries disproportionate weight in the IV calculation. A single off-market fill can swing the quoted IV by several points, with no real change in market view. A standout IV reading on a low-OI strike deserves extra scepticism, not extra excitement.
Why should option sellers avoid illiquid strikes even if the premium looks attractive?
Because the spread is a cost paid twice — once entering, once exiting. On a thin far-OTM strike, that cost can consume a large share of the entire premium collected. The "attractive" premium on paper and the premium you actually realise after slippage can be very different numbers.
How do you check open interest before selling an option?
Look at the OI column on the option chain for your candidate strike and the nearest ATM strikes on the same expiry. A candidate running at a small fraction of the ATM strike's OI is a thin-book warning. It's a prompt to check the spread next, not a liquidity certainty on its own.
Does liquidity change during the week leading up to expiry?
Yes. It typically concentrates and deepens as expiry approaches, especially for NIFTY and SENSEX where expiry-day flow is heaviest. A wing that looks thin on a Monday scan can look tradeable by midweek. That's why we rescan candidate strikes close to execution, rather than acting on a single check days earlier.
Is there a single open interest number that counts as "liquid enough"?
No. Treat it as relative, not absolute. Compare your candidate strike's OI and spread against that day's ATM strike on the same expiry. What counts as sufficient liquidity shifts with volatility, days to expiry, and overall market activity.
Does this liquidity filter apply the same way to NIFTY and SENSEX?
The mechanics are identical — OI, spread as a percentage of premium, and LTP against the mid all mean the same thing on either chain. What changes is the baseline: SENSEX strikes often carry lower absolute OI than their NIFTY equivalents at the same relative distance from ATM, so comparing a SENSEX candidate against a NIFTY threshold number would misread the chain. Always set the ATM baseline on the same underlying you're about to trade, not a number borrowed from the other index.
Should a beginner avoid far-OTM strikes entirely until they understand liquidity?
Not entirely, but a beginner who hasn't yet built the habit of checking OI and spread before every entry is better served sticking closer to ATM for a while. The strikes closest to ATM are consistently the most liquid across almost every session, which makes them more forgiving while you're still building the screening habit described above. Move further out only once the five-point checklist is second nature, and only in a paper account first.
