POP vs POT: Why Your Short Strike Gets Touched More Than You Think
You sell a put with an 85% probability of profit, and within days the market is sitting on your strike. Bad luck? Usually not. The probability of touch (POT) on that same strike was likely close to double the chance of finishing past it. Here’s why, tested on 36 years of SPX highs and lows, and what it means for stops.
See POP, POT and P50 for today’s strikes. Open Lines shows today’s SPX, SPY and QQQ expected move with POP, POT and P50 for short strikes past it, free.
Open the expected move calculator → POP vs POT vs P50 explainedSPX DeskPOP, POT and P50 in plain English
- POP, probability of profit: the chance the trade makes money at expiration. For a short put that’s the chance the price finishes above the strike minus the credit.
- POT, probability of touch: the chance the price touches your short strike at any moment before expiration. Touching isn’t losing, but it’s when stops fire and nerves crack.
- P50: the chance you can buy the trade back for half the credit before expiration, the classic profit-taking exit.
Every trade idea on ETFap shows all three, and the POP vs POT vs P50 page has the formulas.
Why touch is about 2x: the reflection principle
Picture every path the price could take. Any path that finishes below your strike must have touched it first. Now take a path that touched the strike and flip (“reflect”) everything after the touch: a path that ended below becomes one that ended above, equally likely if there’s no drift. So for every touched path that finished below, there’s a twin that touched and finished above. That’s the reflection principle, and it gives the rule of thumb:
Probability of touch ≈ 2 × probability of finishing past the strike
Since a short option’s delta roughly approximates the chance it finishes in the money, a 16-delta put has about a 32% model chance of being touched. Drift, skew and fat tails bend the rule, so I tested it.
Testing it on 36 years of SPX
For every trading day from Jan 2, 1990 to Oct 29, 2026 I took the SPX close, measured the expected move from that day’s VIX, and placed imaginary put strikes 0.5, 1, 1.5 and 2 expected moves below. Then I checked Cboe’s daily highs and lows to see whether each strike was touched intraday, closed below at any point, or finished below:
| Put strike below the close (5 trading days) | Touched intraday | Closed below at any point | Finished below | Touch ÷ finish | Touched but finished above | Model touch / finish |
|---|---|---|---|---|---|---|
| 0.5 expected moves | 43.9% | 32.4% | 20.8% | 2.1× | 53% | 62% / 31% |
| 1 expected move | 18.4% | 12.4% | 8.4% | 2.2× | 55% | 32% / 16% |
| 1.5 expected moves | 6.8% | 4.0% | 2.9% | 2.3× | 57% | 13% / 7% |
| 2 expected moves | 2.3% | 1.4% | 1.1% | 2.1× | 53% | 5% / 2% |
| Put strike below the close (21 trading days) | Touched intraday | Closed below at any point | Finished below | Touch ÷ finish | Touched but finished above | Model touch / finish |
|---|---|---|---|---|---|---|
| 0.5 expected moves | 44.2% | 36.7% | 17.7% | 2.5× | 60% | 62% / 31% |
| 1 expected move | 17.3% | 14.0% | 7.1% | 2.4× | 59% | 32% / 16% |
| 1.5 expected moves | 7.3% | 5.1% | 2.6% | 2.9× | 65% | 13% / 7% |
| 2 expected moves | 3.3% | 2.1% | 0.9% | 3.8× | 74% | 5% / 2% |
The 2x rule held up: at one expected move, touches ran 2.2× finishes over 5 days and 2.4× over 21 days. Over 21 days, a strike one expected move out was touched intraday 17.3% of the time but finished below only 7.1%. The further out and longer the trade, the higher the ratio: a strike that’s rarely reached tends to recover when it is.
It holds on a single day too: a 1-day strike at one expected move was touched 16.4% of the time and finished below 9.0%, so even 0DTE strikes get tagged about twice as often as they lose.
Why the market touches less than the model
The “model” column assumes SPX moves exactly as VIX implies. Real touch rates came in lower at the same distance (17.3% vs 32% for one expected move over 21 days), because VIX usually runs above the volatility SPX actually delivers (selling outside the expected move has the data). That’s the seller’s edge, and it’s why model POT is a conservative planning number, not a forecast. It also varies with the backdrop: see IV rank explained.
Reading a real trade
From the Oct 30, 2026 SPX chain on Open Lines, with strikes just outside each expiry’s expected move. Examples, not recommendations:
| SPX example (Oct 30, 2026 chain, SPX near 7,639) | Credit | POP | POT | P50 |
|---|---|---|---|---|
| Sell the Nov 5, 2026 7525 put | $24.95 | 88% | 29% | 92% |
| Sell the Nov 5, 2026 7525/7500 put spread | $4.25 | 85% | 29% | 89% |
| Sell the Dec 11, 2026 7400 put | $80.90 | 89% | 40% | 94% |
| Sell the Dec 11, 2026 7400/7375 put spread | $4.45 | 85% | 40% | 90% |
The Nov 5, 2026 7525 put had a 88% POP but a 29% POT: about a 1-in-3 chance SPX tags it before expiry. The Dec 11, 2026 put, with more time, had a 40% POT despite a higher POP. Time adds touch risk even when the strike is further away. P50 was high for all of them, so the 50% exit is usually available before a touch.
What it means for stops and adjustments
- Plan for the touch, not just the loss. If POT is 30%, expect your strike to be tested on roughly 3 trades in 10. Decide your action before you enter.
- A touch stop is expensive. At one expected move, 55% (5 days) to 59% (21 days) of touched SPX put strikes still finished above the strike. Stopping on every intraday touch closes many winners at the worst price.
- Prefer a close-based rule. A close below the short strike happened less often than an intraday touch (14.0% vs 17.3% over 21 days at one expected move). The SPX Desk model uses a close below the short strike as its stop.
- Size so a touch doesn’t scare you. If a tested strike tempts you to panic, the position is too big (bankroll rules).
- Take the P50 exit. Closing at half the credit cuts the time your strike is exposed to a touch.
- Covered calls too. POT matters on the call side: a touched covered call strike is a roll decision. The Covered Call & PMCC Tracker shows POT for every suggested call (covered calls vs PMCC).
Sources and method. Cboe daily open/high/low/close for _SPX and closes for _VIX (cdn.cboe.com delayed quotes history), Jan 2, 1990 to Oct 29, 2026, about 9,250 to 9,270 entry days per window. Entry at each day’s close; expected move = close × VIX ÷ 100 × √(N ÷ 252) for N trading days; strikes placed below the close; touches from daily lows (an intraday touch), closes from daily closes. “Model” = driftless lognormal at the entry VIX with no skew: finish = N(−k), touch ≈ 2 × N(−k). Trade examples: Cboe delayed SPX quotes, Oct 30, 2026, bid/ask mids, via Open Lines; POP, POT and P50 are model estimates.
FAQ
What is the difference between POP and POT?
POP (probability of profit) is the chance a trade makes money at expiration. POT (probability of touch) is the chance the price touches your short strike at any time before expiration. A strike can be touched and still expire worthless, so POT is always higher than the chance of finishing past the strike.
Why is probability of touch about double?
It comes from the reflection principle for a random walk: every path that ends below a level had to cross it, and for each crossing path that ends below there is a mirror-image path that crossed and ended above. With no drift, that makes the chance of touching about twice the chance of finishing past the level.
Does the 2x rule hold for SPX?
Roughly. From Jan 2, 1990 to Oct 29, 2026, an SPX put strike one expected move below the close was touched intraday within 5 trading days 18.4% of the time and finished below it 8.4% of the time, a ratio of 2.2. Over 21 days it was 17.3% vs 7.1%.
What is P50?
P50 is the model chance of being able to buy back a short option or spread for half the credit you collected before expiration. Traders who take profits at 50% use it to judge how often that exit will be available.
Should I set a stop when my short strike is touched?
Think it through first. In SPX history, about half or more of touched put strikes still finished above the strike: 55% over 5 days and 59% over 21 days at one expected move. A touch stop exits many trades that would have won; many traders use a close below the strike or a loss multiple instead.
Does delta equal probability of touch?
No. A short option’s delta is roughly the chance it finishes in the money. The chance of touching the strike is roughly double that, so a 16-delta put has about a 32% model chance of being touched.
Why does the market touch strikes less often than the model says?
Implied volatility usually runs above the volatility that actually happens, so model POT built from implied volatility tends to overstate how far the price really travels. That gap is the option seller’s edge, but crashes still happen.
Is this financial advice?
No. It is education from my own process. Options involve substantial risk.
Check the touch odds before you sell. Open Lines shows today’s SPX, SPY and QQQ expected move with POP, POT and P50 for short strikes past it, free.
Open the expected move calculator → POP vs POT vs P50 explainedSPX Desk