1diff --git a/README.md b/README.md
  2index dbe8ff8..5b82e97 100644
  3--- a/README.md
  4+++ b/README.md
  5@@ -32,4 +32,6 @@ arbitrary javascript is executed in the client machine.
  6 
  7 ### Criteria evaluations should escape reg-ex characters: http://stackoverflow.com/questions/3446170/escape-string-for-use-in-javascript-regex
  8 
  9-### Refactor `Util.ts`
 10+### License for all code used.
 11+
 12+### Document the functions pulled in from jStat.
 13\ No newline at end of file
 14diff --git a/src/RawFormulas/Math.ts b/src/RawFormulas/Math.ts
 15index daf72f2..1933bb9 100644
 16--- a/src/RawFormulas/Math.ts
 17+++ b/src/RawFormulas/Math.ts
 18@@ -1385,6 +1385,7 @@ function erf(x) {
 19  * @param values[2] deg_freedom2 - Required. The denominator degrees of freedom.
 20  * @returns {number} inverse of the (right-tailed) F probability distribution
 21  * @constructor
 22+ * TODO: This function needs to be tested more thuroughly.
 23  */
 24 var FINV = function (...values) : number {
 25   function betacf(x, a, b) {
 26@@ -1796,6 +1797,27 @@ var FISHERINV = function (...values) : number {
 27   return (e2y - 1) / (e2y + 1);
 28 };
 29 
 30+/**
 31+ * Calculates the annual effective interest rate given the nominal rate and number of compounding periods per year.
 32+ * @param values[0] nominal_rate - The nominal interest rate per year.
 33+ * @param values[1] periods_per_year - The number of compounding periods per year.
 34+ * @returns {number} annual effective interest rate
 35+ * @constructor
 36+ */
 37+var EFFECT = function (...values) : number {
 38+  ArgsChecker.checkLength(values, 2);
 39+  var rate = TypeCaster.firstValueAsNumber(values[0]);
 40+  var periods = TypeCaster.firstValueAsNumber(values[1]);
 41+  if (rate <= 0) {
 42+    throw new CellError(ERRORS.NUM_ERROR, "Function EFFECT parameter 1 value is " + rate + ". It should be greater than to 0");
 43+  }
 44+  if (periods < 1) {
 45+    throw new CellError(ERRORS.NUM_ERROR, "Function EFFECT parameter 2 value is " + periods + ". It should be greater than or equal to 1");
 46+  }
 47+  periods = Math.floor(periods);
 48+  return Math.pow(1 + rate / periods, periods) - 1;
 49+};
 50+
 51 
 52 export {
 53   ABS,
 54@@ -1819,6 +1841,7 @@ export {
 55   DEVSQ,
 56   DB,
 57   DDB,
 58+  EFFECT,
 59   EVEN,
 60   ERF,
 61   ERFC,
 62diff --git a/src/RawFormulas/RawFormulas.ts b/src/RawFormulas/RawFormulas.ts
 63index 34d5201..1a513cd 100644
 64--- a/src/RawFormulas/RawFormulas.ts
 65+++ b/src/RawFormulas/RawFormulas.ts
 66@@ -23,6 +23,7 @@ import {
 67   DEVSQ,
 68   DB,
 69   DDB,
 70+  EFFECT,
 71   EVEN,
 72   ERF,
 73   ERFC,
 74@@ -125,7 +126,6 @@ var DOLLARFR = Formula["DOLLARFR"];
 75 var EDATE = function (start_date: Date, months) {
 76   return moment(start_date).add(months, 'months').toDate();
 77 };
 78-var EFFECT = Formula["EFFECT"];
 79 var EOMONTH = function (start_date, months) {
 80   var edate = moment(start_date).add(months, 'months');
 81   return new Date(edate.year(), edate.month(), edate.daysInMonth());
 82@@ -136,8 +136,6 @@ var __COMPLEX = {
 83 };
 84 var YEARFRAC = Formula["YEARFRAC"];
 85 
 86-
 87-
 88 export {
 89   __COMPLEX,
 90 
 91diff --git a/tests/FormulasTest.ts b/tests/FormulasTest.ts
 92index 6698913..6df35ea 100644
 93--- a/tests/FormulasTest.ts
 94+++ b/tests/FormulasTest.ts
 95@@ -880,7 +880,31 @@ assertEquals(AND(10), true);
 96 
 97 assertEqualsDates(EDATE(DATE(1992, 6, 24), 1), new Date('7/24/1992'));
 98 
 99+
100+// Test EFFECT
101 assertEquals(EFFECT(0.99, 12), 1.5890167507927795);
102+assertEquals(EFFECT(0.99, 12.111), 1.5890167507927795);
103+assertEquals(EFFECT(0.99, 12.999), 1.5890167507927795);
104+assertEquals(EFFECT("100000", 12.999), 1.123182670038387e+47);
105+assertEquals(EFFECT([100000], [12.999]), 1.123182670038387e+47);
106+catchAndAssertEquals(function() {
107+  EFFECT();
108+}, ERRORS.NA_ERROR);
109+catchAndAssertEquals(function() {
110+  EFFECT(0.99);
111+}, ERRORS.NA_ERROR);
112+catchAndAssertEquals(function() {
113+  EFFECT(-0.99, 12);
114+}, ERRORS.NUM_ERROR);
115+catchAndAssertEquals(function() {
116+  EFFECT(0.99, 0);
117+}, ERRORS.NUM_ERROR);
118+catchAndAssertEquals(function() {
119+  EFFECT(0.99, "str");
120+}, ERRORS.VALUE_ERROR);
121+catchAndAssertEquals(function() {
122+  EFFECT(0.99, []);
123+}, ERRORS.REF_ERROR);
124 
125 assertEqualsDates(EOMONTH(DATE(1992, 6, 24), 1), new Date('7/31/1992'));
126