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V-Lab

PSI 20 Portuguese Stock Index GARCH Volatility Analysis

Volatility prediction for Monday, September 28th, 2026

1 Day

12.76%

decreased by 0.75%

1 Week

13.05%

decreased by 0.46%

1 Month

14.09%

increased by 0.58%

Analysis last updated: Friday, September 25, 2026 at 05:03 PM UTC

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graph of PSI 20 Portuguese Stock Index GARCH

News Impact Curve

How returns affect tomorrow's volatility

Volatility Forecast

How volatility evolves over time

Parameter Estimates

Dec 30, 1992 to Sep 25, 2026

Model Insight

With persistence 0.993, volatility shocks have a half-life of 94 trading days (~0.4 years), close to a unit root, so long-run forecasts are highly sensitive to this estimate.

σ

GARCH Model

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High persistence: persistence 0.993, shock half-life ~94 days
ParamValuet-stat
ωconst0.0195
6.40***
αARCH0.1354
12.44***
βGARCH0.8572
88.34***

0.993

Persistence

94d

Half-life
σ

GARCH Model

Tap to view equation

ParameterValuet-statistic
ω

const

Unconditional variance weight

0.0195
6.40***
α

ARCH

Response to squared shocks

0.1354
12.44***
β

GARCH

Volatility persistence

0.8572
88.34***

Persistence:

0.993

Half-life:

94 days