Index: Riskeer/Common/src/Riskeer.Common.Forms/Helpers/ProbabilityParsingHelper.cs
===================================================================
diff -u
--- Riskeer/Common/src/Riskeer.Common.Forms/Helpers/ProbabilityParsingHelper.cs	(revision 0)
+++ Riskeer/Common/src/Riskeer.Common.Forms/Helpers/ProbabilityParsingHelper.cs	(revision 818104ca78befaa67dbaa0c22de835a438491085)
@@ -0,0 +1,72 @@
+// Copyright (C) Stichting Deltares 2021. All rights reserved.
+//
+// This file is part of Riskeer.
+//
+// Riskeer is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+// 
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <http://www.gnu.org/licenses/>.
+//
+// All names, logos, and references to "Deltares" are registered trademarks of
+// Stichting Deltares and remain full property of Stichting Deltares at all times.
+// All rights reserved.
+
+using System;
+using Riskeer.Common.Forms.Properties;
+using CommonBaseResources = Core.Common.Base.Properties.Resources;
+
+namespace Riskeer.Common.Forms.Helpers
+{
+    /// <summary>
+    /// Helper class to parse probabilities.
+    /// </summary>
+    public static class ProbabilityParsingHelper
+    {
+        private const string returnPeriodNotation = "1/";
+
+        /// <summary>
+        /// Parses a string value to a probability.
+        /// </summary>
+        /// <param name="value">The value to be parsed.</param>
+        /// <returns>A <see cref="double"/> representing a probability.</returns>
+        /// <exception cref="ArgumentException">Thrown when <paramref name="value"/> could not be successfully parsed as a probability.</exception>
+        public static double Parse(string value)
+        {
+            if (string.IsNullOrWhiteSpace(value) || value.Trim() == Resources.RoundedDouble_No_result_dash)
+            {
+                return double.NaN;
+            }
+
+            try
+            {
+                if (!value.StartsWith(returnPeriodNotation))
+                {
+                    return Convert.ToDouble(value);
+                }
+
+                string returnPeriodValue = value.Substring(2).ToLower();
+                return returnPeriodValue != CommonBaseResources.RoundedDouble_ToString_PositiveInfinity.ToLower()
+                           ? 1 / Convert.ToDouble(returnPeriodValue)
+                           : 0.0;
+            }
+            catch (FormatException exception)
+            {
+                throw new ArgumentException(Resources.Probability_Could_not_parse_string_to_probability,
+                                            exception);
+            }
+            catch (OverflowException exception)
+            {
+                throw new ArgumentException(Resources.Probability_Value_too_large,
+                                            exception);
+            }
+        }
+    }
+}
\ No newline at end of file
Index: Riskeer/Common/test/Riskeer.Common.Forms.Test/Helpers/ProbabilityParsingHelperTest.cs
===================================================================
diff -u
--- Riskeer/Common/test/Riskeer.Common.Forms.Test/Helpers/ProbabilityParsingHelperTest.cs	(revision 0)
+++ Riskeer/Common/test/Riskeer.Common.Forms.Test/Helpers/ProbabilityParsingHelperTest.cs	(revision 818104ca78befaa67dbaa0c22de835a438491085)
@@ -0,0 +1,111 @@
+// Copyright (C) Stichting Deltares 2021. All rights reserved.
+//
+// This file is part of Riskeer.
+//
+// Riskeer is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+// 
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <http://www.gnu.org/licenses/>.
+//
+// All names, logos, and references to "Deltares" are registered trademarks of
+// Stichting Deltares and remain full property of Stichting Deltares at all times.
+// All rights reserved.
+
+using System;
+using System.Globalization;
+using NUnit.Framework;
+using Riskeer.Common.Forms.Helpers;
+
+namespace Riskeer.Common.Forms.Test.Helpers
+{
+    [TestFixture]
+    public class ProbabilityParsingHelperTest
+    {
+        [Test]
+        [SetCulture("nl-NL")]
+        [TestCase("1/25", 0.04)]
+        [TestCase("1/2,500", 0.4)]
+        [TestCase("1/2.500", 0.0004)]
+        [TestCase("1e-3", 0.001)]
+        [TestCase("1/1.000", 0.001)]
+        [TestCase("1/0", double.PositiveInfinity)]
+        [TestCase("1/Oneindig", 0.0)]
+        [TestCase("1/oneINdig", 0.0)]
+        [TestCase("1/-1.000", -0.001)]
+        [TestCase("1/-10", -0.1)]
+        [TestCase("1/-2,5", -0.4)]
+        [TestCase("-0,5", -0.5)]
+        [TestCase("-1", -1.0)]
+        [TestCase("-1e-2", -0.01)]
+        public void Parse_ValidStringInDutchCulture_ReturnsExpectedOutput(string value, double expectedProbability)
+        {
+            // Call
+            double parsedProbability = ProbabilityParsingHelper.Parse(value);
+
+            // Assert
+            Assert.AreEqual(expectedProbability, parsedProbability);
+        }
+
+        [Test]
+        [SetCulture("en-US")]
+        [TestCase("1/25", 0.04)]
+        [TestCase("1/2.5", 0.4)]
+        [TestCase("1e-3", 0.001)]
+        [TestCase("1/1,000", 0.001)]
+        [TestCase("1/0", double.PositiveInfinity)]
+        [TestCase("1/Oneindig", 0.0)]
+        [TestCase("1/oneINdig", 0.0)]
+        [TestCase("1/-1,000", -0.001)]
+        [TestCase("1/-10", -0.1)]
+        [TestCase("1/-2.5", -0.4)]
+        [TestCase("-0.5", -0.5)]
+        [TestCase("-1", -1.0)]
+        [TestCase("-1e-2", -0.01)]
+        public void Parse_ValidStringInEnglishCulture_ReturnsExpectedOutput(string value, double expectedProbability)
+        {
+            // Call
+            double parsedProbability = ProbabilityParsingHelper.Parse(value);
+
+            // Assert
+            Assert.AreEqual(expectedProbability, parsedProbability);
+        }
+
+        [Test]
+        public void Parse_ValueDoesNotRepresentProbability_ThrowsArgumentException()
+        {
+            // Setup
+            const string invalidValue = "I'm not a number!";
+
+            // Call
+            TestDelegate call = () => ProbabilityParsingHelper.Parse(invalidValue);
+
+            // Assert
+            var exception = Assert.Throws<ArgumentException>(call);
+            Assert.IsInstanceOf<FormatException>(exception.InnerException);
+            Assert.AreEqual("De waarde kon niet geïnterpreteerd worden als een kans.", exception.Message);
+        }
+
+        [Test]
+        public void Parse_ValueTooLargeToStoreInDouble_ThrowsArgumentException()
+        {
+            // Setup
+            string invalidValue = "1" + double.MaxValue.ToString(CultureInfo.CurrentCulture);
+
+            // Call
+            TestDelegate call = () => ProbabilityParsingHelper.Parse(invalidValue);
+
+            // Assert
+            var exception = Assert.Throws<ArgumentException>(call);
+            Assert.IsInstanceOf<OverflowException>(exception.InnerException);
+            Assert.AreEqual("De waarde is te groot of te klein.", exception.Message);
+        }
+    }
+}
\ No newline at end of file