1diff --git a/DOCS.md b/DOCS.md
  2index c9f4d4c..4a20aed 100644
  3--- a/DOCS.md
  4+++ b/DOCS.md
  5@@ -2058,6 +2058,18 @@
  6 @returns {number} 
  7 @constructor
  8 ```
  9+
 10+### PROB 
 11+
 12+```
 13+  Returns the probability that values in a range are between two limits. Data is the array or range of data in the ample. 
 14+@param range - The array or range of data in the sample. 
 15+@param probability - The array or range of the corresponding probabilities 
 16+@param start - The start value of the interval whose probabilities are to be summed. 
 17+@param end - [OPTIONAL] - The end value of the interval whose probabilities are to be summed. If this parameter is missing, the probability for the start value is calculated 
 18+@returns {number} 
 19+@constructor
 20+```
 21 ## Text
 22 
 23 
 24diff --git a/TODO.md b/TODO.md
 25index 5f1ecd4..7078dd2 100644
 26--- a/TODO.md
 27+++ b/TODO.md
 28@@ -66,7 +66,6 @@ Many of these formulas can be written by allowing the Sheet and Parser to return
 29 * LOGINV
 30 * LOGNORMDIST
 31 * MODE
 32-* PROB
 33 * RANK
 34 * RANK.AVG
 35 * RANK.EQ
 36diff --git a/dist/Formulas/AllFormulas.js b/dist/Formulas/AllFormulas.js
 37index 9eafc38..5acd2b4 100644
 38--- a/dist/Formulas/AllFormulas.js
 39+++ b/dist/Formulas/AllFormulas.js
 40@@ -191,6 +191,7 @@ exports.PERMUT = Statistical_1.PERMUT;
 41 exports.RSQ = Statistical_1.RSQ;
 42 exports.SKEW = Statistical_1.SKEW;
 43 exports.STEYX = Statistical_1.STEYX;
 44+exports.PROB = Statistical_1.PROB;
 45 var Text_1 = require("./Text");
 46 exports.ARABIC = Text_1.ARABIC;
 47 exports.CHAR = Text_1.CHAR;
 48diff --git a/dist/Formulas/Statistical.js b/dist/Formulas/Statistical.js
 49index 14196d3..046b0f9 100644
 50--- a/dist/Formulas/Statistical.js
 51+++ b/dist/Formulas/Statistical.js
 52@@ -1787,3 +1787,43 @@ var STEYX = function (rangeY, rangeX) {
 53     return Math.sqrt((lft - num * num / den) / (n - 2));
 54 };
 55 exports.STEYX = STEYX;
 56+/**
 57+ * Returns the probability that values in a range are between two limits. Data is the array or range of data in the
 58+ * sample.
 59+ * @param range - The array or range of data in the sample.
 60+ * @param probability - The array or range of the corresponding probabilities
 61+ * @param start - The start value of the interval whose probabilities are to be summed.
 62+ * @param end - [OPTIONAL] - The end value of the interval whose probabilities are to be summed. If this parameter is
 63+ * missing, the probability for the start value is calculated
 64+ * @returns {number}
 65+ * @constructor
 66+ */
 67+var PROB = function (range, probability, start, end) {
 68+    ArgsChecker_1.ArgsChecker.checkLengthWithin(arguments, 3, 4, "PROB");
 69+    range = Filter_1.Filter.flattenAndThrow(range);
 70+    probability = Filter_1.Filter.flattenAndThrow(probability);
 71+    if (range.length !== probability.length) {
 72+        throw new Errors_1.NAError("PROB has mismatched argument count " + range.length + " vs " + probability.length + ".");
 73+    }
 74+    var sum = Math_1.SUM(probability);
 75+    if (sum <= 0 || sum > 1) {
 76+        throw new Errors_1.ValueError("Function PROB parameter 2 should sum to 1, but sums to " + sum + ".");
 77+    }
 78+    start = TypeConverter_1.TypeConverter.firstValueAsNumber(start);
 79+    end = (end === undefined) ? start : TypeConverter_1.TypeConverter.firstValueAsNumber(end);
 80+    if (start === end) {
 81+        return (range.indexOf(start) >= 0) ? probability[range.indexOf(start)] : 0;
 82+    }
 83+    var sorted = range.sort(function (a, b) {
 84+        return a - b;
 85+    });
 86+    var n = sorted.length;
 87+    var result = 0;
 88+    for (var i = 0; i < n; i++) {
 89+        if (sorted[i] >= start && sorted[i] <= end) {
 90+            result += probability[range.indexOf(sorted[i])];
 91+        }
 92+    }
 93+    return result;
 94+};
 95+exports.PROB = PROB;
 96diff --git a/src/Formulas/AllFormulas.ts b/src/Formulas/AllFormulas.ts
 97index dc1b6c7..1c85403 100644
 98--- a/src/Formulas/AllFormulas.ts
 99+++ b/src/Formulas/AllFormulas.ts
100@@ -196,7 +196,8 @@ import {
101   PERMUT,
102   RSQ,
103   SKEW,
104-  STEYX
105+  STEYX,
106+  PROB
107 } from "./Statistical";
108 import {
109   ARABIC,
110@@ -467,5 +468,6 @@ export {
111   PERMUT,
112   RSQ,
113   SKEW,
114-  STEYX
115+  STEYX,
116+  PROB
117 }
118\ No newline at end of file
119diff --git a/src/Formulas/Statistical.ts b/src/Formulas/Statistical.ts
120index 756f04c..6db312c 100644
121--- a/src/Formulas/Statistical.ts
122+++ b/src/Formulas/Statistical.ts
123@@ -11,7 +11,7 @@ import {
124   TypeConverter
125 } from "../Utilities/TypeConverter";
126 import {
127-  RefError, NumError, DivZeroError, NAError
128+  RefError, NumError, DivZeroError, NAError, ValueError
129 } from "../Errors";
130 import {
131   SUM,
132@@ -1769,6 +1769,47 @@ var STEYX =  function (rangeY, rangeX) {
133 };
134 
135 
136+/**
137+ * Returns the probability that values in a range are between two limits. Data is the array or range of data in the
138+ * sample.
139+ * @param range - The array or range of data in the sample.
140+ * @param probability - The array or range of the corresponding probabilities
141+ * @param start - The start value of the interval whose probabilities are to be summed.
142+ * @param end - [OPTIONAL] - The end value of the interval whose probabilities are to be summed. If this parameter is
143+ * missing, the probability for the start value is calculated
144+ * @returns {number}
145+ * @constructor
146+ */
147+var PROB =  function (range, probability, start, end?) {
148+  ArgsChecker.checkLengthWithin(arguments, 3, 4, "PROB");
149+  range = Filter.flattenAndThrow(range);
150+  probability = Filter.flattenAndThrow(probability);
151+  if (range.length !== probability.length) {
152+    throw new NAError("PROB has mismatched argument count " + range.length + " vs " + probability.length + ".");
153+  }
154+  var sum = SUM(probability);
155+  if (sum <=0 || sum > 1) {
156+    throw new ValueError("Function PROB parameter 2 should sum to 1, but sums to " + sum + ".");
157+  }
158+  start = TypeConverter.firstValueAsNumber(start);
159+  end = (end === undefined) ? start : TypeConverter.firstValueAsNumber(end);
160+  if (start === end) {
161+    return (range.indexOf(start) >= 0) ? probability[range.indexOf(start)] : 0;
162+  }
163+  var sorted = range.sort(function (a, b) {
164+    return a - b;
165+  });
166+  var n = sorted.length;
167+  var result = 0;
168+  for (var i = 0; i < n; i++) {
169+    if (sorted[i] >= start && sorted[i] <= end) {
170+      result += probability[range.indexOf(sorted[i])];
171+    }
172+  }
173+  return result;
174+};
175+
176+
177 export {
178   AVERAGE,
179   AVERAGEA,
180@@ -1824,5 +1865,6 @@ export {
181   PERMUT,
182   RSQ,
183   SKEW,
184-  STEYX
185+  STEYX,
186+  PROB
187 }
188\ No newline at end of file
189diff --git a/tests/Formulas/StatisticalTest.ts b/tests/Formulas/StatisticalTest.ts
190index 9c4287f..700b319 100644
191--- a/tests/Formulas/StatisticalTest.ts
192+++ b/tests/Formulas/StatisticalTest.ts
193@@ -53,7 +53,8 @@ import {
194   PERMUT,
195   RSQ,
196   SKEW,
197-  STEYX
198+  STEYX,
199+  PROB
200 } from "../../src/Formulas/Statistical";
201 import * as ERRORS from "../../src/Errors";
202 import {
203@@ -1090,4 +1091,26 @@ test("STEYX", function() {
204   catchAndAssertEquals(function() {
205     STEYX.apply(this, [[1, 2, 3], [1, 2, 3], [1, 2, 3]]);
206   }, ERRORS.NA_ERROR);
207+});
208+
209+test("PROB", function() {
210+  assertEquals(PROB([1, 2, 3, 4], [0.25, 0.25, 0.25, 0.25], 3), 0.25);
211+  assertEquals(PROB([1], [1], 3), 0);
212+  assertEquals(PROB([1], [1], 0.1, 100), 1);
213+  assertEquals(PROB([1, 2, 3], [0.25, 0.25, 0.5], 3), 0.5);
214+  assertEquals(PROB([1, 2, 4], [0.25, 0.25, 0.5], 3), 0);
215+  assertEquals(PROB([1, 2, 3], [0.25, 0.25, 0.5], 3, 100), 0.5);
216+  assertEquals(PROB([1, 2, 3], [0.25, 0.25, 0.5], 0.1, 100), 1);
217+  catchAndAssertEquals(function() {
218+    PROB([1, 2, 3, 4], [0.25, 0.25, 0.25], 3);
219+  }, ERRORS.NA_ERROR);
220+  catchAndAssertEquals(function() {
221+    PROB([1, 2, 3, 4], [0.25, 0.25, 0.25, 0.99], 3);
222+  }, ERRORS.VALUE_ERROR);
223+  catchAndAssertEquals(function() {
224+    PROB.apply(this, [[1, 2, 3, 4], [0.25, 0.25, 0.25]]);
225+  }, ERRORS.NA_ERROR);
226+  catchAndAssertEquals(function() {
227+    PROB.apply(this, [[1, 2, 3, 4], [0.25, 0.25, 0.25], 10, 10, 10]);
228+  }, ERRORS.NA_ERROR);
229 });
230\ No newline at end of file
231diff --git a/tests/SheetFormulaTest.ts b/tests/SheetFormulaTest.ts
232index 5ed0f3a..afc6d67 100644
233--- a/tests/SheetFormulaTest.ts
234+++ b/tests/SheetFormulaTest.ts
235@@ -922,6 +922,10 @@ test("Sheet STEYX", function(){
236   assertFormulaEquals('=STEYX([1, 2, 3, 4], [1, 3, 5, 2])', 1.4638501094227998);
237 });
238 
239+test("Sheet PROB", function(){
240+  assertFormulaEquals('=PROB([1, 2, 3, 4], [0.25, 0.25, 0.25, 0.25], 3)', 0.25);
241+});
242+
243 test("Sheet *", function(){
244   assertFormulaEquals('= 10 * 10', 100);
245   assertFormulaEquals('= 10 * 0', 0);