I pull VIX1D from Cboe now

There is a one-day VIX

You know VIX — the "fear index." More precisely, it is expected volatility over the next 30 days.

There is also VIX1D, which Cboe launched on April 24, 2023. As the name says, it covers one day.

	VIX	VIX1D
Window	next 30 days	today
Built from	~30-day options	same-day expiry (0DTE)
Launched	1993	2023

Why it matters: a 30-day ruler measures one day badly.

A big event today gets diluted into a 30-day average. Or today is quiet but VIX is elevated because of an FOMC three weeks out. If you trade same-day expiry, VIX has the wrong window.

---

Turning the number into a range

Both indices are annualized, so to get one day you divide by the square root of the trading days in a year (about 252).

expected 1-day move (1σ) = index × VIX1D(%) ÷ √252

√252 ≈ 15.87

Example — index at 7,800, VIX1D at 9.5:

7,800 × 0.095 ÷ 15.87 ≈ 46.7 points

About ±47 points today. That is the range the market is pricing. It's called the implied move.

One sigma means roughly 68% of days finish inside it. Flip that around: one day in three finishes outside. It is a reference line, not a promise.

---

What if that number is wrong

Everything above is textbook. Here is the part that isn't.

I automated this calculation. Every morning it pulls VIX1D, computes the day's expected range, and I make various judgments against that range.

One day the band came out oddly wide. When I checked, the VIX1D value itself was wrong.

free data source   →  16.69
Cboe official      →   9.49

about 38% apart

The formula was fine. The input was wrong.

Here is what that does to the range:

	VIX1D	computed 1-day range (index 7,800)
bad value	16.69	±82 points
official	9.49	±47 points

±82 and ±47 are different worlds. Every judgment I made against that band that day was built on sand.

---

Why this happens

VIX1D is a relatively new index, launched in 2023.

VIX has been around for thirty years, so every data service gets it right. VIX1D is different: the ticker convention varies by provider, and some services return a different index under the same name. Some fill in something similar when the real value is missing.

And here is the dangerous part — it doesn't throw an error. A perfectly normal-looking number arrives. It's just the wrong one.

---

So this is what I do now

1. Pull VIX1D from Cboe directly. Cboe publishes a daily CSV.
2. If another source is unavoidable, reconcile at least one day against the official value before trusting it.
3. In automation, range-check the input. If VIX1D normally sits between 8 and 15 and a 25 arrives, stop.

---

This isn't really about VIX1D

What I took from this wasn't knowledge about VIX1D. It was a habit.

Suspect the input before you suspect the formula.

Automation makes numbers flow smoothly. They render nicely, nothing errors out. That is exactly why wrong values are harder to catch. When you calculate by hand, a strange number stops you. Automation just carries it forward.

If one input is 38% wrong, everything built on top of it is wrong.

---

Summary

• VIX1D = one-day volatility index (launched 2023-04-24)
• index × VIX1D% ÷ 15.87 = today's expected move (1σ)
• 1σ is a reference line, not a promise — one day in three lands outside it
• 🚨 Check your source. I once received a value 38% off from a free feed.

---

This is an explanation of a volatility calculation and of validating data. It is not a recommendation to trade any security. Your decisions and their outcomes are your own.