Summary. A single total GEX figure mixes options expiring this afternoon with options expiring next quarter. Splitting gamma by expiration shows how much of today's map will still exist tomorrow.
Most gamma exposure discussions use one number: total GEX across the chain. It is a useful summary, but it adds together positions that behave in completely different ways. Gamma in an option that expires at 4:00 p.m. today is not the same kind of exposure as gamma in an option that expires in March. Splitting the map by expiration answers a question the total cannot: how much of today's positioning will still be there tomorrow?
1. Why gamma depends so much on time
For an at-the-money option, gamma is roughly proportional to 1 / (S × σ × √T), where S is spot, σ is implied volatility and T is time to expiration. The important term is the square root of T in the denominator. As expiration approaches, at-the-money gamma rises, and it rises quickly in the final days and hours.
A hypothetical comparison makes the scale clear. Take two at-the-money SPX options with the same implied vol. One has 30 days left, the other a quarter of a trading day. The ratio of their gamma is roughly the square root of the ratio of their time left — and with 30 days against a few hours, the same-day option carries many times the gamma per contract.
The trade-off is that the same-day option's gamma is concentrated. It is enormous at the money and falls away quickly a few strikes out. The 30-day option's gamma is lower at the money but spread across a much wider band of strikes.
2. Three layers in every map
It helps to think of the SPX gamma map as three layers stacked on top of each other.
- Same-day (0DTE). High gamma, narrow band, gone by the close. This layer drives the intraday pins and air pockets near spot and rebuilds every morning. The 0DTE gamma guide covers how it builds and decays.
- Weekly and near-dated. Options expiring over the next few sessions. Less gamma per contract, but it carries from day to day and shapes the walls you see across a week.
- Monthly and quarterly. The large standard expirations. Lower gamma per contract early in the cycle, but often the largest open interest on the board. This layer builds the multi-week walls and becomes dominant as its own expiration approaches.
The total GEX number is the sum of all three. Two days with the same total can have very different structures underneath.
3. The question to ask every morning
The single most useful thing an expiration breakdown tells you is what share of the gamma near spot expires today.
A hypothetical example. On a Tuesday, the map shows a strong call wall at 6,050 and a solid long-gamma regime above a flip at 5,980.
- Case A: most of the gamma at 6,050 comes from monthly options expiring in three weeks. That wall will still exist tomorrow, and the day after. You can plan around it for the week.
- Case B: most of the gamma at 6,050 comes from options expiring today. The wall is real this afternoon — and likely to be much weaker at tomorrow's open, when that open interest is gone.
Same level, same total, completely different implications for anyone holding a position overnight.
4. Why the map looks different every morning
Because the same-day layer expires every afternoon, the map you see at the next morning's open is effectively the residual: the weekly and monthly layers, plus whatever new same-day positioning builds after the bell. That is why the premarket map is usually smoother than the late-session map, and why levels that dominated the previous afternoon can disappear overnight.
It is also why the levels need re-marking after the open. Most of the same-day positioning that will drive the afternoon has not been opened yet at 9:30.
5. Expiration weeks change the balance
As a monthly expiration approaches, the monthly layer's gamma rises for the same reason same-day gamma does: less time left. In the final days before a standard monthly expiry, the monthly open interest can dominate the map near spot. That is the mechanical root of the pinning behavior around monthly OPEX, covered in pin risk mechanics.
After the monthly expiry, that layer is gone. If it was a large share of total gamma, the map can go from heavily pinned to noticeably lighter in a single day. Expiration breakdowns make that visible ahead of time: you can see how much of the map is about to roll off before it happens.
6. Daily expirations made this matter more
SPX now has options expiring every trading day of the week, not just Fridays. That means there is always a same-day layer, and it is often a large one. A few years ago the bulk of near-dated gamma sat in the Friday weekly and the monthly; now every session has an expiring block that builds after the open and disappears at the close. The result is a map that reshapes itself daily. Totals that once moved slowly through the week can now swing from one session to the next, mostly because of what was opened and closed in the same day. Separating that churn from the longer-dated positioning is the main reason to look at gamma by expiration at all.
7. Reading the breakdown in practice
- High share of gamma expiring today: expect strong intraday levels that fade by tomorrow. Trade the walls for today; do not plan the week around them.
- High share in the weekly layer: walls that persist for a few sessions. Useful for swing positioning within the week.
- High share in the next monthly expiry: sticky levels that can govern price for weeks, with a sharp change once that expiry passes.
- A big drop in total gamma after an expiration: a lighter map, wider ranges and less pinning until new open interest builds.
8. A note on sign
An expiration breakdown also shows that different layers can carry opposite signs. It is common for the same-day layer to be positioned one way near spot while the monthly layer sits the other way further out. When the same-day layer expires, the regime near spot can flip even though nothing about the longer-dated positioning changed. That is one reason the gamma flip can move overnight with no news. The wider context for SPX in particular is in SPX gamma exposure explained.
Total GEX tells you the size of the hedging machine. The expiration breakdown tells you how long each part of it will keep running. To see the levels and how they shift through each expiration cycle, see DataFirst's plans.
For educational and informational purposes. Not financial advice; options trading involves substantial risk of loss. All prices in this post are hypothetical.