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V-Lab

CBOE S&P 500 9-Day Volatility Index GAS-GARCH Student T Volatility Analysis

Volatility prediction for Friday, September 18th, 2026

1 Day

229.94%

increased by 43.98%

1 Week

218.88%

increased by 32.92%

1 Month

205.01%

increased by 19.05%

Analysis last updated: Friday, September 18, 2026 at 11:33 AM UTC

Date Range:

from

to

6M ·

1Y ·

2Y ·

5Y ·

10Y ·

All

graph of CBOE S&P 500 9-Day Volatility Index GAS-GARCH-T

News Impact Curve

How returns affect tomorrow's volatility

Volatility Forecast

How volatility evolves over time

Parameter Estimates

Jan 3, 2011 to Sep 11, 2026

Model Insight

Volatility shocks decay with a half-life of 3 trading days, meaning a shock loses half its impact after approximately 3 days. Returns follow a Student-t distribution with v = 5.24 degrees of freedom, capturing fatter tails than a normal distribution.

𝑓

GAS-GARCH-T Model

Tap to view equation

Shock decay: Shocks decay with a 3-day half-lifev = 5.24 · fat tails
ParamValuet-stat
ωconst155.4384
4.89***
αARCH0.1138
2.69***
βGARCH0.7727
12.83***
νDF5.2381
0.80

0.773

Persistence

3d

Half-life
𝑓

GAS-GARCH-T Model

Tap to view equation

ParameterValuet-statistic
ω

const

Unconditional variance weight

155.4384
4.89***
α

ARCH

Response to squared shocks

0.1138
2.69***
β

GARCH

Volatility persistence

0.7727
12.83***
ν

DF

Student-t tail thickness

5.2381
0.80

Persistence:

0.773

Half-life:

3 days