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S&P MidCap 400 Index GAS-GARCH Student T Volatility Analysis

Volatility prediction for Friday, September 25th, 2026

1 Day

12.10%

decreased by 0.36%

1 Week

12.31%

decreased by 0.15%

1 Month

13.06%

increased by 0.60%

Analysis last updated: Thursday, September 24, 2026 at 11:02 PM UTC

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graph of S&P MidCap 400 Index GAS-GARCH-T

News Impact Curve

How returns affect tomorrow's volatility

Volatility Forecast

How volatility evolves over time

Parameter Estimates

Jan 1, 1990 to Sep 18, 2026

Model Insight

Volatility shocks decay with a half-life of 52 trading days, meaning a shock loses half its impact after approximately 52 days. Returns follow a Student-t distribution with v = 10.96 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 52-day half-lifev = 10.96 · fat tails
ParamValuet-stat
ωconst1.3619
2.78***
αARCH0.0884
9.26***
βGARCH0.9866
177.71***
νDF10.9565
1.12

0.987

Persistence

52d

Half-life
𝑓

GAS-GARCH-T Model

Tap to view equation

ParameterValuet-statistic
ω

const

Unconditional variance weight

1.3619
2.78***
α

ARCH

Response to squared shocks

0.0884
9.26***
β

GARCH

Volatility persistence

0.9866
177.71***
ν

DF

Student-t tail thickness

10.9565
1.12

Persistence:

0.987

Half-life:

52 days