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S&P Total Market Index GAS-GARCH Student T Volatility Analysis

Volatility prediction for Monday, September 21st, 2026

1 Day

12.25%

decreased by 0.93%

1 Week

12.50%

decreased by 0.68%

1 Month

13.36%

increased by 0.18%

Analysis last updated: Saturday, September 19, 2026 at 12:02 AM UTC

Date Range:

from

to

6M ·

1Y ·

2Y ·

5Y ·

10Y ·

All

graph of S&P Total Market Index GAS-GARCH-T

News Impact Curve

How returns affect tomorrow's volatility

Volatility Forecast

How volatility evolves over time

Parameter Estimates

Mar 30, 2006 to Sep 18, 2026

Model Insight

Volatility shocks decay with a half-life of 41 trading days, meaning a shock loses half its impact after approximately 41 days. Returns follow a Student-t distribution with v = 6.72 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 41-day half-lifev = 6.72 · fat tails
ParamValuet-stat
ωconst1.3391
1.75*
αARCH0.1082
8.16***
βGARCH0.9831
93.37***
νDF6.7233
1.80*

0.983

Persistence

41d

Half-life
𝑓

GAS-GARCH-T Model

Tap to view equation

ParameterValuet-statistic
ω

const

Unconditional variance weight

1.3391
1.75*
α

ARCH

Response to squared shocks

0.1082
8.16***
β

GARCH

Volatility persistence

0.9831
93.37***
ν

DF

Student-t tail thickness

6.7233
1.80*

Persistence:

0.983

Half-life:

41 days