Index: Ringtoets/MacroStabilityInwards/src/Ringtoets.MacroStabilityInwards.Service/MacroStabilityInwardsSemiProbabilisticCalculationService.cs
===================================================================
diff -u -rda31d7f34c54ec5800146246aa26509a6e78c118 -r977062f457f7e99785741716c660d7afe8e25a11
--- Ringtoets/MacroStabilityInwards/src/Ringtoets.MacroStabilityInwards.Service/MacroStabilityInwardsSemiProbabilisticCalculationService.cs	(.../MacroStabilityInwardsSemiProbabilisticCalculationService.cs)	(revision da31d7f34c54ec5800146246aa26509a6e78c118)
+++ Ringtoets/MacroStabilityInwards/src/Ringtoets.MacroStabilityInwards.Service/MacroStabilityInwardsSemiProbabilisticCalculationService.cs	(.../MacroStabilityInwardsSemiProbabilisticCalculationService.cs)	(revision 977062f457f7e99785741716c660d7afe8e25a11)
@@ -37,6 +37,7 @@
         private readonly double contribution;
 
         private readonly double stabilityFactor;
+        private readonly double modelFactor;
         private double macroStabilityInwardsProbability;
         private double macroStabilityInwardsReliability;
 
@@ -54,19 +55,22 @@
         /// <param name="assessmentSectionLength">The length of the assessment section.</param>
         /// <param name="contribution">The contribution of macro stability inwards to the total failure.</param>
         /// <param name="stabilityFactor">The stability factor of the calculation result.</param>
+        /// <param name="modelFactor">The model factor of the calculation result.</param>
         private MacroStabilityInwardsSemiProbabilisticCalculationService(double norm,
                                                                          double constantA,
                                                                          double constantB,
                                                                          double assessmentSectionLength,
                                                                          double contribution,
-                                                                         double stabilityFactor)
+                                                                         double stabilityFactor,
+                                                                         double modelFactor)
         {
             this.norm = norm;
             this.constantA = constantA;
             this.constantB = constantB;
             this.assessmentSectionLength = assessmentSectionLength;
             this.contribution = contribution;
             this.stabilityFactor = stabilityFactor;
+            this.modelFactor = modelFactor;
         }
 
         /// <summary>
@@ -107,7 +111,8 @@
                 probabilityAssessmentInput.A,
                 probabilityAssessmentInput.B,
                 probabilityAssessmentInput.SectionLength,
-                contribution / 100, calculation.Output.FactorOfStability);
+                contribution / 100, calculation.Output.FactorOfStability,
+                generalInput.ModelFactor);
 
             calculator.Calculate();
 
@@ -151,7 +156,7 @@
         /// <returns>The estimated reliability based on the stability factor.</returns>
         private double CalculateEstimatedReliability()
         {
-            return (6.21 * stabilityFactor) - 2.88;
+            return ((stabilityFactor / modelFactor) - 0.41) / 0.15;
         }
     }
 }
\ No newline at end of file
Index: Ringtoets/MacroStabilityInwards/test/Ringtoets.MacroStabilityInwards.Service.Test/MacroStabilityInwardsSemiProbabilisticCalculationServiceTest.cs
===================================================================
diff -u -rda31d7f34c54ec5800146246aa26509a6e78c118 -r977062f457f7e99785741716c660d7afe8e25a11
--- Ringtoets/MacroStabilityInwards/test/Ringtoets.MacroStabilityInwards.Service.Test/MacroStabilityInwardsSemiProbabilisticCalculationServiceTest.cs	(.../MacroStabilityInwardsSemiProbabilisticCalculationServiceTest.cs)	(revision da31d7f34c54ec5800146246aa26509a6e78c118)
+++ Ringtoets/MacroStabilityInwards/test/Ringtoets.MacroStabilityInwards.Service.Test/MacroStabilityInwardsSemiProbabilisticCalculationServiceTest.cs	(.../MacroStabilityInwardsSemiProbabilisticCalculationServiceTest.cs)	(revision 977062f457f7e99785741716c660d7afe8e25a11)
@@ -178,10 +178,11 @@
         }
 
         [Test]
-        [TestCase(0.75)]
-        [TestCase(0.55)]
-        [TestCase(0.30)]
-        public void MacroStabilityInwardsReliability_DifferentInputs_ReturnsExpectedValues(double factorOfStability)
+        [TestCase(0.75, 1.98365)]
+        [TestCase(0.55, 0.72579)]
+        [TestCase(0.30, -0.84654)]
+        public void MacroStabilityInwardsReliability_DifferentInputs_ReturnsExpectedValues(double factorOfStability,
+                                                                                           double expectedResult)
         {
             // Setup
             var random = new Random(21);
@@ -204,13 +205,13 @@
             RoundedDouble result = calculation.SemiProbabilisticOutput.MacroStabilityInwardsReliability;
 
             // Assert
-            Assert.AreEqual(GetDerivedEstimatedReliability(factorOfStability), result, result.GetAccuracy());
+            Assert.AreEqual(expectedResult, result, result.GetAccuracy());
         }
 
         [Test]
-        [TestCase(0.75, 0.037743005)]
-        [TestCase(0.55, 0.2961520790)]
-        [TestCase(0.30, 0.845423280)]
+        [TestCase(0.75, 0.023647)]
+        [TestCase(0.55, 0.233984)]
+        [TestCase(0.30, 0.801374)]
         public void MacroStabilityInwardsProbability_DifferentInputs_ReturnsExpectedValues(double factorOfStability,
                                                                                            double expectedResult)
         {
@@ -239,11 +240,6 @@
             Assert.AreEqual(expectedResult, result, accuracy); // Probability is a derived output from reliability, hence accuracy is determined by the accuracy of the reliability
         }
 
-        private static double GetDerivedEstimatedReliability(double stabilityFactor)
-        {
-            return (6.21 * stabilityFactor) - 2.88;
-        }
-
         private static double GetRequiredProbability(double norm,
                                                      double contribution,
                                                      double constantA,