1diff --git a/src/RawFormulas/Financial.ts b/src/RawFormulas/Financial.ts
  2index de49da0..6338c4e 100644
  3--- a/src/RawFormulas/Financial.ts
  4+++ b/src/RawFormulas/Financial.ts
  5@@ -212,7 +212,90 @@ var EFFECT = function (...values) : number {
  6   return Math.pow(1 + rate / periods, periods) - 1;
  7 };
  8 
  9+/**
 10+ * Calculates the cumulative principal paid over a range of payment periods for an investment based on constant-amount
 11+ * periodic payments and a constant interest rate.
 12+ * @param values[0] rate - The interest rate.
 13+ * @param values[1] number_of_periods - The number of payments to be made.
 14+ * @param values[2] present_value - The current value of the annuity.
 15+ * @param values[3] first_period - The number of the payment period to begin the cumulative calculation. must be greater
 16+ * than or equal to 1.
 17+ * @param values[4] last_period - The number of the payment period to end the cumulative calculation, must be greater
 18+ * than first_period.
 19+ * @param values[5] end_or_beginning - Whether payments are due at the end (0) or beginning (1) of each period
 20+ * @returns {number} cumulative principal
 21+ * @constructor
 22+ */
 23+var CUMPRINC = function (...values) : number {
 24+  function pmt(rate, periods, present, future, type) {
 25+    var result;
 26+    if (rate === 0) {
 27+      result = (present + future) / periods;
 28+    } else {
 29+      var term = Math.pow(1 + rate, periods);
 30+      if (type) {
 31+        result = (future * rate / (term - 1) + present * rate / (1 - 1 / term)) / (1 + rate);
 32+      } else {
 33+        result = future * rate / (term - 1) + present * rate / (1 - 1 / term);
 34+      }
 35+    }
 36+    return -result;
 37+  }
 38+
 39+  function fv(rate, periods, payment, value, type) {
 40+    var result;
 41+    if (rate === 0) {
 42+      result = value + payment * periods;
 43+    } else {
 44+      var term = Math.pow(1 + rate, periods);
 45+      if (type) {
 46+        result = value * term + payment * (1 + rate) * (term - 1.0) / rate;
 47+      } else {
 48+        result = value * term + payment * (term - 1) / rate;
 49+      }
 50+    }
 51+    return -result;
 52+  }
 53+
 54+  ArgsChecker.checkLength(values, 6);
 55+  var rate = TypeCaster.firstValueAsNumber(values[0]);
 56+  var periods = TypeCaster.firstValueAsNumber(values[1]);
 57+  var value = TypeCaster.firstValueAsNumber(values[2]);
 58+  var start = TypeCaster.firstValueAsNumber(values[3]);
 59+  if (start < 1) {
 60+    throw new CellError(ERRORS.NUM_ERROR, "Function CUMPRINC parameter 4 value is " + start + ". It should be greater than or equal to 1.");
 61+  }
 62+  var end = TypeCaster.firstValueAsNumber(values[4]);
 63+  if (end < 1) {
 64+    throw new CellError(ERRORS.NUM_ERROR, "Function CUMPRINC parameter 5 value is " + end + ". It should be greater than or equal to 1.");
 65+  }
 66+  if (end < start) {
 67+    throw new CellError(ERRORS.NUM_ERROR, "Function CUMPRINC parameter 5 value is " + end + ". It should be greater than or equal to " + start + ".");
 68+  }
 69+  var type = TypeCaster.firstValueAsBoolean(values[5]);
 70+
 71+  var payment = pmt(rate, periods, value, 0, type);
 72+  var principal = 0;
 73+  if (start === 1) {
 74+    if (type) {
 75+      principal = payment;
 76+    } else {
 77+      principal = payment + value * rate;
 78+    }
 79+    start++;
 80+  }
 81+  for (var i = start; i <= end; i++) {
 82+    if (type) {
 83+      principal += payment - (fv(rate, i - 2, payment, value, 1) - payment) * rate;
 84+    } else {
 85+      principal += payment - fv(rate, i - 1, payment, value, 0) * rate;
 86+    }
 87+  }
 88+  return principal;
 89+};
 90+
 91 export {
 92+  CUMPRINC,
 93   DB,
 94   DDB,
 95   DOLLAR,
 96diff --git a/src/RawFormulas/RawFormulas.ts b/src/RawFormulas/RawFormulas.ts
 97index 4481168..2427a1f 100644
 98--- a/src/RawFormulas/RawFormulas.ts
 99+++ b/src/RawFormulas/RawFormulas.ts
100@@ -73,6 +73,7 @@ import {
101   DELTA
102 } from "./Engineering";
103 import {
104+  CUMPRINC,
105   DB,
106   DDB,
107   DOLLAR,
108@@ -124,7 +125,6 @@ import * as ERRORS from "../Errors"
109 var ACCRINT = Formula["ACCRINT"];
110 var CONVERT = Formula["CONVERT"];
111 var CUMIPMT = Formula["CUMIPMT"];
112-var CUMPRINC = Formula["CUMPRINC"];
113 var DATE = Formula["DATE"];
114 var DATEVALUE = function (dateString: string) : Date {
115   return new Date(dateString);
116diff --git a/src/RawFormulas/Statistical.ts b/src/RawFormulas/Statistical.ts
117index 15026f4..b876e6a 100644
118--- a/src/RawFormulas/Statistical.ts
119+++ b/src/RawFormulas/Statistical.ts
120@@ -777,7 +777,6 @@ var COUNTA = function (...values) : number {
121   return count;
122 };
123 
124-
125 export {
126   AVERAGE,
127   AVERAGEA,
128diff --git a/tests/FormulasTest.ts b/tests/FormulasTest.ts
129index c89eceb..8f86bee 100644
130--- a/tests/FormulasTest.ts
131+++ b/tests/FormulasTest.ts
132@@ -703,9 +703,35 @@ catchAndAssertEquals(function() {
133 }, ERRORS.NA_ERROR);
134 
135 
136+// Test CUMIPMT
137 assertEquals(CUMIPMT(0.12, 12, 100, 1, 5, 0), -54.39423242396348);
138 
139+
140+// Test CUMPRINC
141+assertEquals(CUMPRINC(0.12, 12, 100, 1, 5, false), -26.324171373034403);
142 assertEquals(CUMPRINC(0.12, 12, 100, 1, 5, 0), -26.324171373034403);
143+assertEquals(CUMPRINC(0.12, 12, 100, 1, 5, true), -34.21801015449499);
144+assertEquals(CUMPRINC(0.12, 12, 100, 1, 5, -11), -34.21801015449499);
145+catchAndAssertEquals(function() {
146+  CUMPRINC(0.12, 12, 100, 1, 5, []);
147+}, ERRORS.REF_ERROR);
148+catchAndAssertEquals(function() {
149+  CUMPRINC(0.12, 12, 100, 0, 5, false);
150+}, ERRORS.NUM_ERROR);
151+catchAndAssertEquals(function() {
152+  CUMPRINC(0.12, 12, 100, 3, 1, false);
153+}, ERRORS.NUM_ERROR);
154+catchAndAssertEquals(function() {
155+  CUMPRINC();
156+}, ERRORS.NA_ERROR);
157+catchAndAssertEquals(function() {
158+  CUMPRINC(0.12, 12, 100, 1, 5, true, 55);
159+}, ERRORS.NA_ERROR);
160+catchAndAssertEquals(function() {
161+  CUMPRINC(0.12, 12, 100, 1, 5);
162+}, ERRORS.NA_ERROR);
163+
164+
165 
166 assertEqualsDates(DATE(1992, 6, 24), new Date("6/24/1992"));
167 assertEqualsDates(DATE(1992, 13, 24), new Date("1/24/1993"));