Put/Call Ratio: 20 Years of Cboe Data Against SPY's Next Month
The put/call ratio is the number of put option contracts traded divided by the number of call contracts traded over the same period, usually one day. Cboe publishes total, index and equity versions daily, and traders read a high ratio as heavy demand for protection and a low one as heavy call buying.
Every trading day, Cboe publishes how many put and call contracts changed hands, and one division turns those counts into one of the oldest sentiment gauges in the options market. The ratio is simple. Reading it is not, because the number it produces has drifted a long way over two decades. This page works through the arithmetic for 25 September 2026, then lines up 5,005 days of Cboe ratios against what SPY did over the following week, month and quarter.
How it works
Puts traded divided by calls traded. A put gains when the underlying falls, a call when it rises, so a day with more put volume than call volume produces a ratio above 1.0, and a day dominated by calls produces one below it. Most published versions count contracts traded that day. A version built on open interest counts contracts still open instead, and it moves far more slowly.
Cboe splits the count by product. The equity ratio covers options on individual stocks. Since 11 June 2012, according to the note in Cboe’s own history file, it has excluded options on exchange-traded products, which Cboe reports separately. The index ratio covers options on indexes such as the S&P 500, where institutions buy puts as insurance, so it usually sits higher. The total ratio adds everything together.
How traders read it
The contrarian reading is the usual one. A high ratio says traders are paying for protection, which tends to happen after prices have already fallen; a low ratio says call buyers are crowding in, which tends to happen after a run up. Traders who use it as a contrarian gauge treat extremes in either direction as a sign that one side is overextended.
The source matters. These figures are Cboe’s, and its history file labels them as Cboe exchange volume, so they are not a count of every US options venue. A different source can print a different number for the same day.
Why the level keeps moving
A fixed threshold does not travel. A reading of 0.60 was below the yearly median of 2008 and above that of 2021, as the data further down shows. A rule written as “above 0.70 is fearful” would have fired far more often in some years than others for reasons that had nothing to do with fear.
Ranking against the recent past removes most of the drift. The test on this page places each day against the 252 trading days before it, about a year, and calls a day extreme only when it is higher, or lower, than 90% of them.
A worked example
On Friday 25 September 2026, Cboe’s equity options traded 1,536,751 puts and 2,949,196 calls. The equity ratio is 1,536,751 / 2,949,196 = 0.5211, published as 0.52. Across all products the counts were 5,968,172 puts and 7,971,692 calls, for a total ratio of 5,968,172 / 7,971,692 = 0.7487, or 0.75.
Smoothing the week. The five equity readings from 21 to 25 September were 0.5291, 0.4656, 0.4555, 0.5544 and 0.5211. Their average is 2.5257 / 5 = 0.5051, a little under the day’s own figure. Many traders watch a five- or ten-day average for exactly this reason: single days jump around.
Placing it against the past year. Of the 252 trading days from 24 September 2025 to 24 September 2026, 69 had a lower equity ratio than 0.5211. That puts Friday at roughly the 27th percentile, an ordinary reading. To land in the top 10% of that year, a day would have needed a ratio above about 0.69; the highest in 2026 so far was 0.90, on 18 March.
The original data
The sample. Cboe’s equity and total put/call ratios for every trading day from 1 November 2006 to 25 September 2026: 3,253 days from Cboe’s history files, which end on 4 October 2019, and 1,752 days from its daily statistics files after that, 5,005 in all. For every day, the ratio recomputed from the put and call counts matched the two-decimal ratio Cboe published. The full daily series, with SPY’s forward returns alongside, is in the put/call file.
The yearly median equity ratio has swung widely. It was 0.76 in 2008, fell to 0.50 in 2020 and 0.47 in 2021 as call buying surged, climbed back to 0.66 in 2023, and is 0.58 for 2026 so far, across 184 days. The total ratio followed the same path at a higher level, from 1.00 in 2008 to 0.81 in 2021 and 0.87 this year.
The extremes. The median equity ratio over all 5,005 days was 0.62. The lowest single day was 0.32, on 14 April 2010, and the highest was 2.40, on 28 December 2022, when Cboe counted 2,636,382 equity puts against 1,099,137 calls. The yearly medians list the day count behind every year.
The test. From 2 November 2007, when a full year of history first existed, each day was ranked against its previous 252 days. SPY’s closing price was then measured 5, 21 and 63 trading days later. Returns are price only, without dividends.
What followed the highest readings. Days in the top 10% of their own past year, 546 with a full 21-session window, saw a median SPY change of +2.24% over the next 21 sessions, against +1.52% for all 4,732 days, and 66.5% of those windows ended higher, against 65.9%. Over five sessions the medians were +0.63% and +0.38%. Over 63 sessions the medians were 3.80% and 3.78%, almost the same, and the share that ended higher was lower after a high reading, 68.3% against 72.4%.
What followed the lowest readings. The bottom 10%, 579 days, saw a 21-session median of +1.46% and 67.9% of windows higher, close to the all-day figures. The 3,607 days in between had +1.46% and 65.5%. Low readings did not come before weaker markets in this sample.
The difference shrank over time. Split at 2015, the top-10% days had a 21-session median of +2.60% against +1.34% for middle days from 2007 to 2014, but +1.86% against +1.54% from 2015 to 2026, with fewer of those windows ending higher, 65.0% against 67.6%. The bucket table has all three horizons.
Why none of this is a signal. The 21-session windows overlap, so neighboring days share most of their future. High readings bunch together in selloffs: of the 547 top-10% days, 92 fell in 2022, 59 in 2011 and 53 in 2015, so they reflect far fewer separate episodes than the count suggests. And a gap of under one percentage point in the median, with no gap in how often SPY rose, is well within what a handful of sharp rebounds can produce.
When it fails
The baseline moves under it. The 2021 median of 0.47 would have looked like extreme complacency by 2008 standards, and it lasted a whole year while SPY rose. Any fixed level eventually stops meaning what it once did.
Volume is not intent. A put bought to hedge a stock the trader owns is not a bet against the market, and a call sold against shares adds call volume without being bullish. The ratio counts contracts, not why they traded, and it counts them equally whether each one is worth $5 or $5,000.
One day can be an outlier. The 2.40 reading on 28 December 2022 was more than twice any typical level, and the data files show the counts, not the reason. A single spike deserves a check of the underlying volumes before it is read as a mood.
Fear can be early. High readings arrive during declines, and declines can keep going; the lower share of rising 63-session windows after high readings is a reminder that a gauge built on protection buying can flag a bottom well before one forms.
Related
The put option page explains the contract on the top of the fraction and why it is bought both to speculate and to insure. The VIX reads the same fear from option prices rather than volumes. And open interest covers the slower-moving count that some versions of this ratio use instead of daily volume.
I use the put/call ratio as a note about positioning, next to price, never as the reason for a trade. I compare today’s reading with the past year’s range rather than with a fixed number, because the level itself has moved so much.
— Michael Whitman
This page is educational, not financial advice. Test every idea on your own charts before risking money.