Rolling versus fixed strike
On a fixed-strike straddle chart the strike is chosen once. If the index drifts away, that straddle becomes in- or out-of-the-money and its premium reflects directional exposure as well as volatility.
On a rolling chart the strike is re-selected as spot moves, so each point is the straddle that was at the money at that moment. The line is closer to a pure measure of what at-the-money options cost, and a fall in the line means decay or lower volatility, not that spot has run away from your strike.
The trade-off: a strike change adds a small step to the series. Do not read a single step as a volatility move; read the trend across many points.
What the overlays add
| Overlay | What it is | How to read it |
|---|---|---|
| Straddle premium | ATM call plus put at the rolling strike | The core line: decay, spikes and recoveries |
| VWAP | Volume-weighted average of the premium for the session | A reference for whether premium is trading rich or cheap to its own session average |
| Spot | Underlying price on the right axis | Shows whether a premium spike came with a price move or without one |
| Futures and futures VWAP | Nearest futures price and its average | Spot-futures basis and whether futures is leading or lagging |
Reading an intraday session
- Opening range (first 30 minutes). The opening straddle sets the session's baseline. A large opening premium relative to recent sessions signals an event or gap being priced.
- Mid-session slope. In range-bound sessions the line drifts down below VWAP as decay dominates. A flat line in a quiet market means something is offsetting decay, often rising IV.
- Spikes without a price move. A jump in premium while spot is flat points to volatility being repriced, often on news or a large order in the options themselves.
- Spikes with a price move. If spot is moving hard, the ATM strike rolls and the premium rises with gamma. Check the call/put split to see which leg is doing the work.
- Late session. In the last hour premium decay accelerates and sensitivity to spot increases, so the line becomes more erratic.
Adding context
Pair the premium with the put-call ratio around the ATM strikes to see whether open interest is leaning toward puts or calls, and with the premium as a percentage of spot to compare days and underlyings. The 1-day, 3-day and 7-day views show whether today's level is high or low against the recent week.
See the straddle chart guide for how premium relates to the expected move and the implied volatility guide for what drives it.
Limits
- VWAP is a descriptive average, not a prediction. Premium crossing it is information about the session so far.
- Stale prints. If a leg has not traded recently its last price can lag, which distorts the combined line.
- No costs or P&L. The chart does not include brokerage, taxes or slippage, and a position's result depends on its own entry.