1diff --git a/DOCS.md b/DOCS.md
  2index 44a9ed9..a7ae0bb 100644
  3--- a/DOCS.md
  4+++ b/DOCS.md
  5@@ -614,6 +614,19 @@
  6 @param type - [OPTIONAL defaults to 0] Defines whether the payment is due at the beginning (1) or the end (0) of a period. 
  7 @constructor
  8 ```
  9+
 10+### RATE 
 11+
 12+```
 13+  Returns the constant interest rate per period of an annuity. 
 14+@param periods - The total number of periods, during which payments are made (payment period). 
 15+@param paymentPerPeriod - The constant payment (annuity) paid during each period. 
 16+@param presentValue - The cash value in the sequence of payments 
 17+@param futureValue - [OPTIONAL defaults to 0] The future value, which is reached at the end of the periodic payments. 
 18+@param beginningOrEnd - [OPTIONAL defaults to 0] Defines whether the payment is due at the beginning (1) or the end (0) of a period. 
 19+@param guessRate - [OPTIONAL] - Determines the estimated value of the interest with iterative calculation. 
 20+@constructor
 21+```
 22 ## Info
 23 
 24 
 25diff --git a/TODO.md b/TODO.md
 26index fe68aca..d31123a 100644
 27--- a/TODO.md
 28+++ b/TODO.md
 29@@ -88,6 +88,5 @@ Many of these formulas can be written by allowing the Sheet and Parser to return
 30 * PRICE
 31 * PRICEDISC
 32 * PRICEMAT
 33-* RATE
 34 * RECEIVED
 35 * YIELD
 36diff --git a/dist/Formulas/AllFormulas.js b/dist/Formulas/AllFormulas.js
 37index fbb5f3d..56af867 100644
 38--- a/dist/Formulas/AllFormulas.js
 39+++ b/dist/Formulas/AllFormulas.js
 40@@ -148,6 +148,7 @@ exports.FV = Financial_1.FV;
 41 exports.PPMT = Financial_1.PPMT;
 42 exports.FVSCHEDULE = Financial_1.FVSCHEDULE;
 43 exports.PV = Financial_1.PV;
 44+exports.RATE = Financial_1.RATE;
 45 var Statistical_1 = require("./Statistical");
 46 exports.AVERAGE = Statistical_1.AVERAGE;
 47 exports.AVERAGEA = Statistical_1.AVERAGEA;
 48diff --git a/dist/Formulas/Financial.js b/dist/Formulas/Financial.js
 49index 2018ab1..ebb4a67 100644
 50--- a/dist/Formulas/Financial.js
 51+++ b/dist/Formulas/Financial.js
 52@@ -752,3 +752,71 @@ var PV = function (rate, periods, paymentPerPeriod, future, type) {
 53     }
 54 };
 55 exports.PV = PV;
 56+/**
 57+ * Returns the constant interest rate per period of an annuity.
 58+ * @param periods - The total number of periods, during which payments are made (payment period).
 59+ * @param paymentPerPeriod - The constant payment (annuity) paid during each period.
 60+ * @param presentValue - The cash value in the sequence of payments
 61+ * @param futureValue - [OPTIONAL defaults to 0] The future value, which is reached at the end of the periodic payments.
 62+ * @param beginningOrEnd - [OPTIONAL defaults to 0] Defines whether the payment is due at the beginning (1) or the end
 63+ * (0) of a period.
 64+ * @param guessRate - [OPTIONAL] - Determines the estimated value of the interest with iterative
 65+ * calculation.
 66+ * @constructor
 67+ */
 68+var RATE = function (periods, paymentPerPeriod, presentValue, futureValue, beginningOrEnd, guessRate) {
 69+    ArgsChecker_1.ArgsChecker.checkLengthWithin(arguments, 3, 6, "RATE");
 70+    periods = TypeConverter_1.TypeConverter.firstValueAsNumber(periods);
 71+    if (periods < 1) {
 72+        throw new Errors_1.NumError("Function RATE parameter 1 value is" + periods + ", but it should be greater than 0.");
 73+    }
 74+    paymentPerPeriod = TypeConverter_1.TypeConverter.firstValueAsNumber(paymentPerPeriod);
 75+    presentValue = TypeConverter_1.TypeConverter.firstValueAsNumber(presentValue);
 76+    futureValue = MoreUtils_1.isDefined(futureValue) ? TypeConverter_1.TypeConverter.firstValueAsNumber(futureValue) : 0;
 77+    beginningOrEnd = MoreUtils_1.isDefined(beginningOrEnd) ? TypeConverter_1.TypeConverter.firstValueAsNumber(beginningOrEnd) : 0;
 78+    guessRate = MoreUtils_1.isDefined(guessRate) ? TypeConverter_1.TypeConverter.firstValueAsNumber(guessRate) : 0.1;
 79+    // Sets the limits for possible guesses to any
 80+    // number between 0% and 100%
 81+    var lowLimit = 0;
 82+    var highLimit = 1;
 83+    var guess = guessRate;
 84+    // Defines a tolerance of up to +/- 0.00005% of pmt, to accept
 85+    // the solution as valid.
 86+    var tolerance = Math.abs(0.00000005 * paymentPerPeriod);
 87+    // Tries at most 40 times to find a solution within the tolerance.
 88+    for (var i = 0; i < 40; i++) {
 89+        // Resets the balance to the original pv.
 90+        var balance = presentValue;
 91+        // Calculates the balance at the end of the loan, based
 92+        // on loan conditions.
 93+        for (var j = 0; j < periods; j++) {
 94+            if (beginningOrEnd == 0) {
 95+                // Interests applied before payment
 96+                balance = balance * (1 + guess) + paymentPerPeriod;
 97+            }
 98+            else {
 99+                // Payments applied before insterests
100+                balance = (balance + paymentPerPeriod) * (1 + guess);
101+            }
102+        }
103+        // Returns the guess if balance is within tolerance.  If not, adjusts
104+        // the limits and starts with a new guess.
105+        if (Math.abs(balance + futureValue) < tolerance) {
106+            return guess;
107+        }
108+        else if (balance + futureValue > 0) {
109+            // Sets a new highLimit knowing that
110+            // the current guess was too big.
111+            highLimit = guess;
112+        }
113+        else {
114+            // Sets a new lowLimit knowing that
115+            // the current guess was too small.
116+            lowLimit = guess;
117+        }
118+        // Calculates the new guess.
119+        guess = (highLimit + lowLimit) / 2;
120+    }
121+    throw new Errors_1.NumError("RATE attempted to complete but it was not able to.");
122+};
123+exports.RATE = RATE;
124diff --git a/src/Formulas/AllFormulas.ts b/src/Formulas/AllFormulas.ts
125index d70f881..0e7718f 100644
126--- a/src/Formulas/AllFormulas.ts
127+++ b/src/Formulas/AllFormulas.ts
128@@ -152,7 +152,8 @@ import {
129   FV,
130   PPMT,
131   FVSCHEDULE,
132-  PV
133+  PV,
134+  RATE
135 } from "./Financial";
136 import {
137   AVERAGE,
138@@ -521,5 +522,6 @@ export {
139   ROMAN,
140   TEXT,
141   FVSCHEDULE,
142-  PV
143+  PV,
144+  RATE
145 }
146\ No newline at end of file
147diff --git a/src/Formulas/Financial.ts b/src/Formulas/Financial.ts
148index 457457f..168c205 100644
149--- a/src/Formulas/Financial.ts
150+++ b/src/Formulas/Financial.ts
151@@ -13,7 +13,7 @@ import {
152   YEARFRAC
153 } from "./Date";
154 import {Filter} from "../Utilities/Filter";
155-import {isUndefined} from "../Utilities/MoreUtils";
156+import {isDefined, isUndefined} from "../Utilities/MoreUtils";
157 
158 
159 /**
160@@ -766,6 +766,78 @@ let PV = function (rate, periods, paymentPerPeriod, future?, type?) {
161 };
162 
163 
164+/**
165+ * Returns the constant interest rate per period of an annuity.
166+ * @param periods - The total number of periods, during which payments are made (payment period).
167+ * @param paymentPerPeriod - The constant payment (annuity) paid during each period.
168+ * @param presentValue - The cash value in the sequence of payments
169+ * @param futureValue - [OPTIONAL defaults to 0] The future value, which is reached at the end of the periodic payments.
170+ * @param beginningOrEnd - [OPTIONAL defaults to 0] Defines whether the payment is due at the beginning (1) or the end
171+ * (0) of a period.
172+ * @param guessRate - [OPTIONAL] - Determines the estimated value of the interest with iterative
173+ * calculation.
174+ * @constructor
175+ */
176+let RATE = function (periods, paymentPerPeriod, presentValue, futureValue?, beginningOrEnd?, guessRate?) {
177+  ArgsChecker.checkLengthWithin(arguments, 3, 6, "RATE");
178+  periods = TypeConverter.firstValueAsNumber(periods);
179+  if (periods < 1) {
180+    throw new NumError("Function RATE parameter 1 value is" + periods + ", but it should be greater than 0.");
181+  }
182+  paymentPerPeriod = TypeConverter.firstValueAsNumber(paymentPerPeriod);
183+  presentValue = TypeConverter.firstValueAsNumber(presentValue);
184+  futureValue = isDefined(futureValue) ? TypeConverter.firstValueAsNumber(futureValue) : 0;
185+  beginningOrEnd = isDefined(beginningOrEnd) ? TypeConverter.firstValueAsNumber(beginningOrEnd) : 0;
186+  guessRate = isDefined(guessRate) ? TypeConverter.firstValueAsNumber(guessRate) : 0.1;
187+
188+  // Sets the limits for possible guesses to any
189+  // number between 0% and 100%
190+  let lowLimit = 0;
191+  let highLimit = 1;
192+  let guess = guessRate;
193+
194+  // Defines a tolerance of up to +/- 0.00005% of pmt, to accept
195+  // the solution as valid.
196+  let tolerance = Math.abs(0.00000005 * paymentPerPeriod);
197+
198+  // Tries at most 40 times to find a solution within the tolerance.
199+  for (let i = 0; i < 40; i++) {
200+    // Resets the balance to the original pv.
201+    let balance = presentValue;
202+
203+    // Calculates the balance at the end of the loan, based
204+    // on loan conditions.
205+    for (let j = 0; j < periods; j++ ) {
206+      if (beginningOrEnd == 0) {
207+        // Interests applied before payment
208+        balance = balance * (1 + guess) + paymentPerPeriod;
209+      } else {
210+        // Payments applied before insterests
211+        balance = (balance + paymentPerPeriod) * (1 + guess);
212+      }
213+    }
214+
215+    // Returns the guess if balance is within tolerance.  If not, adjusts
216+    // the limits and starts with a new guess.
217+    if (Math.abs(balance + futureValue) < tolerance) {
218+      return guess;
219+    } else if (balance + futureValue > 0) {
220+      // Sets a new highLimit knowing that
221+      // the current guess was too big.
222+      highLimit = guess;
223+    } else  {
224+      // Sets a new lowLimit knowing that
225+      // the current guess was too small.
226+      lowLimit = guess;
227+    }
228+
229+    // Calculates the new guess.
230+    guess = (highLimit + lowLimit) / 2;
231+  }
232+  throw new NumError("RATE attempted to complete but it was not able to.");
233+};
234+
235+
236 export {
237   ACCRINT,
238   CUMPRINC,
239@@ -788,5 +860,6 @@ export {
240   FV,
241   PPMT,
242   FVSCHEDULE,
243-  PV
244+  PV,
245+  RATE
246 }
247\ No newline at end of file
248diff --git a/tests/Formulas/FinancialTest.ts b/tests/Formulas/FinancialTest.ts
249index cd5ba32..10cede9 100644
250--- a/tests/Formulas/FinancialTest.ts
251+++ b/tests/Formulas/FinancialTest.ts
252@@ -20,7 +20,8 @@ import {
253   FV,
254   PPMT,
255   FVSCHEDULE,
256-  PV
257+  PV,
258+  RATE
259 } from "../../src/Formulas/Financial";
260 import {
261   DATE
262@@ -500,4 +501,29 @@ test("PV", function() {
263   catchAndAssertEquals(function() {
264     PV.apply(this, [0, 1, 2, 3, 4, 5]);
265   }, ERRORS.NA_ERROR);
266+});
267+
268+
269+test("RATE", function() {
270+  assertEquals(RATE(12, -100, 400, 0, 0, 0.1), 0.22893307069316507);
271+  assertEquals(RATE(360, -665.3, 99000), 0.005916521358085446);
272+  assertEquals(RATE(360, -958.63, 192000), 0.0036458502960158515);
273+  assertEquals(RATE(180, -1302.96, 192000), 0.0022917255526408564);
274+  assertEquals(RATE(360, -889.19, 192000), 0.0031250616819306744);
275+  assertEquals(RATE(360, -1145.8, 240000), 0.003333353153720964);
276+  assertEquals(RATE(360, -665.3, 99000, 10), 0.00591642102735932);
277+  assertEquals(RATE(12, -100, 400, 100), 0.2225948800332845);
278+  assertEquals(RATE(360, -665.3, 99000, 10, 1), 0.005965913048930816);
279+  catchAndAssertEquals(function() {
280+    RATE(0, -100, 400, 10);
281+  }, ERRORS.NUM_ERROR);
282+  catchAndAssertEquals(function() {
283+    RATE(12, -100, 400, 1000000);
284+  }, ERRORS.NUM_ERROR);
285+  catchAndAssertEquals(function() {
286+    RATE.apply(this, [0, 1]);
287+  }, ERRORS.NA_ERROR);
288+  catchAndAssertEquals(function() {
289+    RATE.apply(this, [1, 2, 3, 4, 5, 6, 7]);
290+  }, ERRORS.NA_ERROR);
291 });
292\ No newline at end of file
293diff --git a/tests/SheetFormulaTest.ts b/tests/SheetFormulaTest.ts
294index 4bbb5ef..5cb1477 100644
295--- a/tests/SheetFormulaTest.ts
296+++ b/tests/SheetFormulaTest.ts
297@@ -1029,6 +1029,10 @@ test("Sheet PV", function(){
298   assertFormulaEquals('=PV(2, 12, 100)', -49.99990591617884);
299 });
300 
301+test("Sheet RATE", function(){
302+  assertFormulaEquals('=RATE(12, -100, 400, 100)', 0.2225948800332845);
303+});
304+
305 test("Sheet parsing error", function(){
306   assertFormulaEqualsError('= 10e', PARSE_ERROR);
307   assertFormulaEqualsError('= SUM(', PARSE_ERROR);