Skip to main content
V-Lab
V-Lab

S&P 500 Growth Index GAS-GARCH Student T Volatility Analysis

Volatility prediction for Tuesday, September 22nd, 2026

1 Day

17.31%

increased by 2.78%

1 Week

17.35%

increased by 2.82%

1 Month

17.52%

increased by 2.99%

Analysis last updated: Monday, September 21, 2026 at 11:01 PM UTC

Date Range:

from

to

6M ·

1Y ·

2Y ·

5Y ·

10Y ·

All

graph of S&P 500 Growth Index GAS-GARCH-T

News Impact Curve

How returns affect tomorrow's volatility

Volatility Forecast

How volatility evolves over time

Parameter Estimates

Oct 29, 1992 to Sep 18, 2026

Model Insight

With persistence 0.991, volatility shocks have a half-life of 76 trading days (~0.3 years), close to a unit root, so long-run forecasts are highly sensitive to this estimate. Returns follow a Student-t distribution with v = 7.54 degrees of freedom, capturing fatter tails than a normal distribution.

𝑓

GAS-GARCH-T Model

Tap to view equation

High persistence: persistence 0.991, shock half-life ~76 daysv = 7.54 · fat tails
ParamValuet-stat
ωconst1.5237
1.48
αARCH0.0881
9.58***
βGARCH0.9909
149.91***
νDF7.5351
1.80*

0.991

Persistence

76d

Half-life
𝑓

GAS-GARCH-T Model

Tap to view equation

ParameterValuet-statistic
ω

const

Unconditional variance weight

1.5237
1.48
α

ARCH

Response to squared shocks

0.0881
9.58***
β

GARCH

Volatility persistence

0.9909
149.91***
ν

DF

Student-t tail thickness

7.5351
1.80*

Persistence:

0.991

Half-life:

76 days