Chart traders draw support and resistance from past prices: levels where buying or selling turned the market before. Option traders have a second source: the option chain. The strikes where the most option contracts are open often act as levels the market finds hard to cross during an expiry. This guide explains why, how to read those levels, and how they shift and fail.
The idea is simple. The strike with the most put open interest is treated as support, and the strike with the most call open interest as resistance.
Why open interest creates levels
In index options, most of the open interest that stays open is held by option sellers (writers). They collect premium and keep it only if the option expires worthless:
- A trader who sells the NIFTY 25,000 put wins if NIFTY stays above 25,000 until expiry.
- A trader who sells the NIFTY 25,500 call wins if NIFTY stays below 25,500.
When huge amounts of puts are sold at one strike, a lot of money is betting that the price holds above it. Those sellers often defend the level: as the price falls towards it, some buy futures to hedge, which slows the fall. The same happens in reverse with calls. Add the hedging of market makers (see gamma exposure) and the result is that heavy strikes tend to act like soft walls. Soft, because they bend and sometimes break.
A worked example
Suppose NIFTY is at 25,230 on the Monday of an expiry week, and the nearest-expiry chain looks like this (OI in lakh contracts):
| Strike | Call OI | Put OI |
|---|---|---|
| 24,900 | 12 | 58 |
| 25,000 | 25 | 112 |
| 25,100 | 30 | 70 |
| 25,200 | 55 | 66 |
| 25,300 | 78 | 34 |
| 25,400 | 84 | 18 |
| 25,500 | 131 | 10 |
The most put OI is at 25,000 (1.12 crore contracts): the market's main support for this expiry. The most call OI is at 25,500 (1.31 crore): the main resistance. Many traders would describe the expected range as 25,000 to 25,500, with 25,300 to 25,400 as a layer of smaller resistance on the way up.
Round numbers (25,000, 25,500) almost always attract the most OI, because that is where traders like to sell. That is partly why these levels coincide with familiar chart levels.
The same reading works for BANKNIFTY, where strikes are wider apart. With BANKNIFTY near 56,000, the heaviest put OI might sit at 55,000 and the heaviest call OI at 57,000, giving a wider band in points but a similar band in percentage terms. Because BANKNIFTY moves more in a day than NIFTY, its walls are tested and broken more often, so its levels deserve a little less trust.
Levels from the whole chain or near the money?
There are two ways to pick the levels, and both are used:
- Whole-chain maximum: the single strike with the most call OI and the single strike with the most put OI across every strike of the expiry. These are the big, slow levels, usually 200 to 500 points from NIFTY. They define the range sellers expect for the expiry.
- Near-the-money maximum: the heaviest strikes within a few strikes of the price. These change during the day and matter more for intraday trading.
When both point to the same strike, that strike is a stronger level. When the near-the-money wall is much smaller than the whole-chain wall further away, expect the nearer one to give way first.
A live example: today's OI levels
Here are the strikes with the most call and put open interest on NIFTY's nearest expiry right now:
Measure the distance from NIFTY to each level. If the index sits near the support strike, put writers are close to being tested; if it sits midway, both sides are comfortable. Here is the part of the chain around the money, which shows the closer, smaller walls:
The bold numbers mark the heaviest strikes within this slice. They are often nearer to the price than the whole-chain maximum, and they matter more for intraday moves.
How the levels shift
OI levels are not fixed for the week. They move as traders adjust, and the shift is often more informative than the level itself:
- Support moving up: put writing grows at higher strikes (the biggest put OI moves from 25,000 to 25,100 to 25,200). Sellers are following a rising market, a bullish sign.
- Resistance moving down: call writing grows at lower strikes. Sellers are pressing down on a weak market.
- Range narrowing: support moving up and resistance moving down at the same time. Sellers expect a quiet expiry near the middle, often near max pain.
- Wall dissolving: the heaviest call strike losing OI fast as the price approaches. Sellers are giving up, and a break becomes more likely. The strike OI tracker guide shows how to watch this.
What makes a level stronger or weaker
- Size relative to neighbours. 1.3 crore at one strike with 80 lakh on either side is a clear wall. 1.3 crore with 1.2 crore next door is a broad zone, not a line.
- Fresh additions. A level where OI was added today is more current than one built a week ago.
- Distance to expiry. Levels matter most in the last two or three days of the expiry, when option sellers' profit depends on them.
- Agreement with the chart. When the heaviest put strike also sits near a previous swing low or a pivot point, more traders are watching the same level.
How traders use OI levels
- Setting a range: option sellers often sell strikes outside the support and resistance levels, aiming to profit if the index stays inside.
- Placing stops: some traders place stops just beyond the main OI level, on the idea that a break means the sellers were wrong.
- Judging breakouts: a move through a big call strike while call OI there collapses (short covering) can run quickly as sellers buy back.
- Combining views: PCR, max pain, gamma walls and OI levels all come from the same chain. When they agree, the picture is clearer.
When OI levels fail
- News and gaps. An overnight event can open the index beyond a wall, and the sellers then rush to cover, which makes the move bigger.
- Expiry day. Gamma is very high near expiry, so a level can hold all morning and break in minutes in the afternoon.
- Hedging OI. Large put OI can be portfolio protection bought by investors rather than sold by bulls; it is not support in the same sense.
- Thin stock options. For most single stocks, option OI is too small for these levels to carry much weight.
Treat OI levels as a map of where sellers have placed their bets. The market respects them often enough to make them worth watching, and breaks them often enough that they should never be the only reason for a trade.