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State Street SPDR S&P 500 ETF Trust GAS-GARCH Student T Volatility Analysis

Volatility prediction for Tuesday, September 29th, 2026

1 Day

12.43%

increased by 0.33%

1 Week

12.59%

increased by 0.49%

1 Month

13.17%

increased by 1.07%

Analysis last updated: Monday, September 28, 2026 at 09:55 PM UTC

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graph of State Street SPDR S&P 500 ETF Trust GAS-GARCH-T

News Impact Curve

How returns affect tomorrow's volatility

Volatility Forecast

How volatility evolves over time

Parameter Estimates

Jan 29, 1993 to Sep 25, 2026

Model Insight

Volatility shocks decay with a half-life of 62 trading days, meaning a shock loses half its impact after approximately 62 days. Returns follow a Student-t distribution with v = 6.81 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 62-day half-lifev = 6.81 · fat tails
ParamValuet-stat
ωconst1.3452
1.67*
αARCH0.0922
10.29***
βGARCH0.9889
139.07***
νDF6.8102
2.21**

0.989

Persistence

62d

Half-life
𝑓

GAS-GARCH-T Model

Tap to view equation

ParameterValuet-statistic
ω

const

Unconditional variance weight

1.3452
1.67*
α

ARCH

Response to squared shocks

0.0922
10.29***
β

GARCH

Volatility persistence

0.9889
139.07***
ν

DF

Student-t tail thickness

6.8102
2.21**

Persistence:

0.989

Half-life:

62 days