iqrc = "IQRCoefficient" /. ChartElementData["BoxWhisker", "Options"];

1.5

fences = {Quartiles[data][[1]] - iqrc InterquartileRange[data ], 
   Quartiles[data][[3]] + iqrc InterquartileRange[data ]};

outliers = Select[Not[fences[[1]] <= # <= fences[[2]]] &]@data

{-3.0844, -3.4005}

which matches the vertical coordinates of outlier glyphs:

Cases[BoxWhiskerChart[data, "Outliers", PerformanceGoal -> "Speed"], 
 Inset[_, {_, a_}] :> a, All]

{-3.0844, -3.4005}

iqrc = "IQRCoefficient" /. ChartElementData["BoxWhisker", "Options"];

1.5

fences = Quartiles[data][[{1, 3}]] + {-1, 1} iqrc InterquartileRange[data]

outliers = Select[Not @* Between[fences]] @ data

{-3.0844, -3.4005}

which matches the vertical coordinates of outlier glyphs:

Cases[BoxWhiskerChart[data, "Outliers", PerformanceGoal -> "Speed"], 
 Inset[_, {_, a_}] :> a, All]

{-3.0844, -3.4005}

iqrc = "IQRCoefficient" /. ChartElementData["BoxWhisker", "Options"];

1.5

fences = {Quartiles[data][[1]] - iqrc InterquartileRange[data ], 
   Quartiles[data][[3]] + iqrc InterquartileRange[data ]};

outliers = Select[Not[fences[[1]] <= # <= fences[[2]]] &]@data

{-3.0844, -3.4005}

which matches the vertical coordinates of outlier glyphs:

Cases[BoxWhiskerChart[data, "Outliers", 
  PerformanceGoal -> "Speed"], _Inset, All]

{Inset[[FilledSmallCircle], {0.696057, -3.0844}],
Inset[[FilledSmallCircle], {0.696057, -3.4005}]}

iqrc = "IQRCoefficient" /. ChartElementData["BoxWhisker", "Options"];

1.5

fences = {Quartiles[data][[1]] - iqrc InterquartileRange[data ], 
   Quartiles[data][[3]] + iqrc InterquartileRange[data ]};

outliers = Select[Not[fences[[1]] <= # <= fences[[2]]] &]@data

{-3.0844, -3.4005}

which matches the vertical coordinates of outlier glyphs:

Cases[BoxWhiskerChart[data, "Outliers", PerformanceGoal -> "Speed"], 
 Inset[_, {_, a_}] :> a, All]

{-3.0844, -3.4005}