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V-Lab

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

Volatility prediction for Monday, August 24th, 2026

1 Day

11.83%

decreased by 0.72%

1 Week

12.05%

decreased by 0.50%

1 Month

12.65%

increased by 0.10%

Analysis last updated: Saturday, August 22, 2026 at 01:42 PM UTC

Date Range:

from

to

6M ·

1Y ·

2Y ·

5Y ·

10Y ·

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graph of Vanguard S&P 500 Index ETF GAS-GARCH-T

News Impact Curve

How returns affect tomorrow's volatility

Volatility Forecast

How volatility evolves over time

Parameter Estimates

Nov 8, 2012 to Aug 21, 2026

Model Insight

Volatility shocks decay with a half-life of 14 trading days, meaning a shock loses half its impact after approximately 14 days. Returns follow a Student-t distribution with v = 8.77 degrees of freedom, capturing fatter tails than a normal distribution.

𝑓

GAS-GARCH-T Model

Tap to view equation

ParameterValuet-statistic
ω

const

Unconditional variance weight

0.7717
16.52***
α

ARCH

Response to squared shocks

0.1114
21.48***
β

GARCH

Volatility persistence

0.9504
255.70***
ν

DF

Student-t tail thickness

8.7704
3.80***

Persistence:

0.950

Half-life:

14 days