V-Lab
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
News Impact Curve
How returns affect tomorrow's volatilityVolatility Forecast
How volatility evolves over timeParameter Estimates
Mar 30, 2006 to Sep 18, 2026Model 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
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Shock decay: Shocks decay with a 41-day half-lifev = 6.72 · fat tails
| Param | Value | t-stat |
|---|---|---|
| ωconst | 1.3391 | 1.75* |
| αARCH | 0.1082 | 8.16*** |
| βGARCH | 0.9831 | 93.37*** |
| νDF | 6.7233 | 1.80* |
0.983
Persistence41d
Half-life𝑓
GAS-GARCH-T Model
Tap to view equation
| Parameter | Value | t-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
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