A Named Vendor Metric, Not a Generic Term
The Sizzle Index is a thinkorswim metric: the ratio of the current day's combined put and call option volume on an underlying to the arithmetic mean of daily put and call volume over the prior five sessions. A reading of 1.00 means today matches the five-day average and 4.00 means four times it. Unlike "unusual volume", which means whatever the person saying it wants it to mean, it is one specific number from one specific platform, defined in the thinkorswim Learning Center. The unusual options activity hub shows session volume aggregated by ticker, expiry and call or put, over the strikes we track, delayed at least 15 minutes.
A reading of 0.50 is half the average, and thinkorswim also computes call-only and put-only versions, built the same way against the matching five-day call or put average, which lets you see whether an active tape is skewed to one side.
The Five-Day Window Is the Whole Story
The lookback is short, which makes the metric responsive and also self-erasing. A big day enters the denominator for the following five sessions, so sustained elevated activity decays back toward 1.00 while the activity itself continues.
Work it through with round numbers. Say a name averages 10,000 contracts a day. Today it trades 40,000, so the Sizzle Index prints 4.00. If tomorrow is another 40,000-contract day, the trailing average has risen to 16,000 and the same 40,000 contracts now read 2.50. A third identical day lifts the average to 22,000 and drops the reading to about 1.82. Nothing changed in the market. The denominator caught up.
The consequence is that Sizzle detects a change in activity, not a level of it. It is at its most informative on the first day of something and quietly stops describing a regime that persists.
What a High Reading Does Not Tell You
It says nothing about direction. Volume counts contracts traded, and every contract traded has a buyer and a seller; a 6.00 reading is equally consistent with heavy call buying, heavy call selling, and a large spread that prints both sides at once.
It says nothing about whether positions opened or closed. Volume and open interest answer different questions, and it is the pair that tells you whether a busy session added exposure or unwound it. Our note on volume versus open interest covers how to read them together.
And because the ratio is scale-free, it flatters illiquid names. A ticker that normally trades 200 contracts a day and then trades 1,200 prints a 6.00, and 1,200 contracts is not institutional anything. Read the ratio next to the absolute contract count: a 1.6 on a name that usually trades 300,000 contracts is by far the more interesting event.
Much of what any such screen catches is calendar rather than information. Earnings dates, index rebalances, dividend-related flows around ex-dates and large expirations all produce mechanical volume spikes that were on the schedule a week earlier.
Building the Same Idea Yourself
Nothing about the construction is proprietary, it is relative volume with a five-session denominator. If you want the concept without the platform, the design questions are the same three every time. How long a lookback? Longer is steadier and slower to fire. What absolute volume floor do you require before a reading counts? That single filter kills most illiquid false positives. And how does the day's volume compare with the open interest already outstanding in the series doing the trading?
SquawkFlow does not publish a Sizzle Index; the term belongs to thinkorswim. What our options flow hub shows is the raw material, delayed volume and prior open interest by ticker, expiry and call or put, which you can compare yourself, and our write-up on scanning for unusual option volume covers the filters that make any relative-volume screen survivable in live markets.
Educational content, not financial advice. See our risk disclosure.