Call Writing and Put Writing: What Option Writers' Open Interest Tells You

Put writing means selling a put option, and call writing means selling a call. The writer collects the premium up front and takes on the obligation that comes with it, which is why writers are the most useful people to watch in an option chain. Every open contract has a buyer and a writer, but the writer is the one whose money is at stake if the index travels through the strike, so the strikes where puts and calls are being written heavily tend to become the floors and ceilings everyone talks about. This guide explains what put writing and call writing mean in plain terms, why written strikes act as levels, how to tell fresh writing from buying in the open interest, what covering looks like, and what writing does not tell you.

What put writing means

A put option gives its buyer the right to sell the index at the strike price on expiry. The person who sells that put, the writer, receives the premium immediately and agrees to pay the difference if the index finishes below the strike. So put writing is a bet that the index will stay above the strike, or at least not fall far below it. The most a put writer can make is the premium received; the loss grows point for point once the index falls below the strike minus that premium.

A simple example, with round numbers: NIFTY is at 22,650 and a trader writes the 22,500 put for ₹100. With a lot of 65 units, that is ₹6,500 received per lot. If NIFTY finishes anywhere above 22,500, the put expires worthless and the writer keeps the ₹6,500. The break-even is 22,400. If NIFTY finishes at 22,300, the put is worth 200 at expiry, and the writer has lost 100 points, or ₹6,500 per lot. Because that loss can be large, writers post margin with their broker, while buyers only pay the premium.

What call writing means

Call writing is the mirror image. A call gives its buyer the right to buy the index at the strike, so the call writer receives the premium and pays out if the index finishes above the strike. Call writing is a bet that the index will stay below the strike. The writer’s gain is capped at the premium, and the loss in theory has no ceiling, because there is no limit to how far an index can rise.

Put writing vs call writing

Read the two together and you get the basic map of an option chain: heavy put writing below the index, heavy call writing above it, and the index trading in the corridor between.

Why put writing builds a floor

Writers have the obligation, so they act when the index comes near their strike. A put writer who sees the index falling toward the strike can buy back the put, buy futures as a hedge, or roll the position lower. Each of those means buying something as the price falls, which is a source of demand near the strike. When thousands of contracts are written at one strike, that demand is concentrated, and the strike behaves like support. The mechanism for call writing is the same in reverse: call writers hedge by buying as the index climbs toward their strike, and if the index does push through, their buying can add to the move.

That is why the strike with the most put open interest is usually labelled support and the strike with the most call open interest resistance, as on the summary chips of the option chain. It is a tendency created by real flows, not a promise. The support and resistance guide covers how those levels hold and how they fail, and the open interest chart shows the whole ladder of written strikes at once.

How to spot fresh put writing in the open interest

Open interest going up at a strike tells you new contracts were opened there, but not by whom: a new contract is created when a fresh buyer meets a fresh writer. The clue is the premium. When open interest rises while the premium falls, sellers were in control of the trade, and the usual reading is fresh writing, known as short build-up. When open interest rises while the premium rises, buyers were pushing, and the reading is long build-up.

So fresh put writing shows up as put open interest rising with the put premium falling, which usually happens when the index is steady or rising. Fresh call writing shows up as call open interest rising while the call premium falls, which usually happens when the index is steady or falling. The OI build-up guide covers the same four states for futures.

Who is doing the writing

The exchange publishes, every evening among its derivatives reports, how many index option contracts each class of participant holds long and short: foreign institutions, proprietary desks, domestic institutions, and clients, the last group being the broad mass of other traders. That report shows who is a net writer. On 5 October 2026, clients were net writers of about 6.35 lakh index put contracts, while foreign institutions were net writers of about 3.66 lakh index calls and net buyers of about 5.88 lakh index puts. In other words, the put writing that day came mostly from clients, while foreign institutions were writing calls and holding puts. The participant-wise open interest guide explains the report, and the FII long short ratio covers the futures side of the same data.

When writers cover

Covering is the writer closing the position by buying the option back. In the open interest it shows as the count falling while the premium rises. Call writers covering into a rally is the classic way a ceiling gives way: the writers buy back their calls, the buying lifts the premium further, and the strike that capped the index stops doing so. Put writers covering into a fall is the same story under the price: the floor is being pulled.

Picture the 23,000 put as the strike with the most put open interest, with NIFTY sliding toward it. If its open interest keeps growing as the index approaches, the writers are adding: they are defending the level. If its open interest starts falling while the put premium climbs, the writers are leaving, and support at 23,000 is weaker than the total still suggests. The change in open interest says more than the total; the change in OI guide is about exactly that.

What put writing cannot tell you

• It is a reading, not a fact about intent. Premium falling while open interest rises makes writing the likely story, but nothing in the public data says who started each trade.
• Writers are often hedged. A put writer may hold futures, a spread or another option against the position, so a written strike is not a clean bet on direction.
• Far out-of-the-money writing is mostly premium collection. Puts written 1,000 points below the index say little about where the index will trade this week.
• Intraday open interest is provisional. The exchange’s official end-of-day figure can differ slightly from the last intraday reading.
• Levels break. Writers with deep pockets are wrong regularly. A written strike tells you where pressure sits, not what the index will do, and none of this is a reason on its own to buy or sell anything.

A worked reading

The figure above is the last hour of a day when NIFTY fell 1.64 percent to 23,063.10. Across the strikes selected on Trending OI, call open interest had grown by about 5.98 crore since the open while put open interest had shrunk by about 66 lakh. On a falling day, with call premiums falling, that is fresh call writing above the index; the shrinking put side says put writers were stepping back as the floor came under pressure. Put the two together and the picture is writers leaning bearish all afternoon, which is what the Diff in OI column and its bearish pills record row after row. It describes what writers did that day; it does not say what the next day would bring.

Where to read call writing and put writing in OIData

• The Option Chain shows each strike’s open interest and today’s change, and the coloured stripe on every OI cell names its build-up, short build-up being fresh writing.
• OI Stats draws call and put open interest by strike as bars, with today’s change shaded; its PE − CE view shows at a glance which strikes are put-heavy and which are call-heavy.
• Trending OI adds up call and put open interest changes since the open across the strikes you pick, row by row through the session.
• Strike History shows one strike’s build-up label day by day, so you can see whether a wall was written over many sessions or in one burst.
• The FII / DII page shows which participants are net writers of index calls and puts.

Put writing FAQ

What does put writing mean? Selling a put option: the writer receives the premium and pays out if the index finishes below the strike at expiry.

Is put writing bullish? It is a view that the index will stay above the strike, so it leans neutral to bullish. Heavy put writing below the index is usually read as support.

What does call writing mean? Selling a call option: the writer receives the premium and pays out if the index finishes above the strike. It leans neutral to bearish, and heavy call writing above the index is read as resistance.

Which is riskier, put writing or call writing? Both can lose far more than the premium received. A call writer’s loss has no upper limit in theory; a put writer’s loss is limited only by the index falling to zero, which in practice is also very large.

How can I tell whether puts are being written or bought? Look at open interest and premium together: open interest up with the premium down reads as writing, open interest up with the premium up as buying.

Takeaways

• Put writing is selling puts: the writer collects the premium and needs the index to stay above the strike. Call writing is the mirror image above the price.
• Heavy put writing tends to act as a floor and heavy call writing as a ceiling, because writers hedge and defend near their strikes.
• Fresh writing shows as open interest rising while the premium falls; covering shows as open interest falling while the premium rises.
• The participant-wise report shows who the net writers are; on 5 October 2026 clients were the big index put writers.
• A written strike is pressure, not a promise: read the change in open interest, not only the total.