diff --git a/Maths/Factorial.js b/Maths/Factorial.js
index 29b416a67e..9b77b8d8f3 100644
--- a/Maths/Factorial.js
+++ b/Maths/Factorial.js
@@ -19,18 +19,18 @@ const calcRange = (num) => {
 
 const calcFactorial = (num) => {
   if (num === 0) {
-    return 'The factorial of 0 is 1.'
+    return 1
   }
   if (num < 0) {
-    return 'Sorry, factorial does not exist for negative numbers.'
+    throw Error('Sorry, factorial does not exist for negative numbers.')
   }
   if (!num) {
-    return 'Sorry, factorial does not exist for null or undefined numbers.'
+    throw Error('Sorry, factorial does not exist for null or undefined numbers.')
   }
   if (num > 0) {
     const range = calcRange(num)
     const factorial = range.reduce((a, c) => a * c, 1)
-    return `The factorial of ${num} is ${factorial}`
+    return factorial
   }
 }
 
diff --git a/Maths/test/Factorial.test.js b/Maths/test/Factorial.test.js
index a065194774..1f5da42bb6 100644
--- a/Maths/test/Factorial.test.js
+++ b/Maths/test/Factorial.test.js
@@ -2,30 +2,20 @@ import { calcFactorial } from '../Factorial'
 
 describe('calcFactorial', () => {
   it('should return a statement for value "0"', () => {
-    expect(calcFactorial(0)).toBe('The factorial of 0 is 1.')
+    expect(calcFactorial(0)).toBe(1)
   })
 
-  it('should return a statement for "null" and "undefined"', () => {
-    const nullFactorial = calcFactorial(null)
-    const undefinedFactorial = calcFactorial(undefined)
-
-    expect(nullFactorial).toBe(
-      'Sorry, factorial does not exist for null or undefined numbers.'
-    )
-    expect(undefinedFactorial).toBe(
-      'Sorry, factorial does not exist for null or undefined numbers.'
-    )
+  it('should throw error for "null" and "undefined"', () => {
+    expect(() => { calcFactorial(null) }).toThrow(Error)
+    expect(() => { calcFactorial(undefined) }).toThrow(Error)
   })
 
-  it('should not support negative numbers', () => {
-    const negativeFactorial = calcFactorial(-5)
-    expect(negativeFactorial).toBe(
-      'Sorry, factorial does not exist for negative numbers.'
-    )
+  it('should throw error for negative numbers', () => {
+    expect(() => { calcFactorial(-1) }).toThrow(Error)
   })
 
   it('should return the factorial of a positive number', () => {
     const positiveFactorial = calcFactorial(3)
-    expect(positiveFactorial).toBe('The factorial of 3 is 6')
+    expect(positiveFactorial).toBe(6)
   })
 })
diff --git a/String/CountSubstrings.js b/String/CountSubstrings.js
new file mode 100644
index 0000000000..f936f8eab0
--- /dev/null
+++ b/String/CountSubstrings.js
@@ -0,0 +1,29 @@
+/**
+ * @function countSubstrings
+ * @description Given a string of words or phrases, count the occurrences of a substring
+ * @param {String} str - The input string
+ * @param {String} substring - The substring
+ * @return {Number} - The number of substring occurrences
+ * @example countSubstrings("This is a string", "is") => 2
+ * @example countSubstrings("Hello", "e") => 1
+ */
+
+const countSubstrings = (str, substring) => {
+  if (typeof str !== 'string' || typeof substring !== 'string') {
+    throw new TypeError('Argument should be string')
+  }
+
+  if (substring.length === 0) return str.length + 1
+
+  let count = 0
+  let position = str.indexOf(substring)
+
+  while (position > -1) {
+    count++
+    position = str.indexOf(substring, position + 1)
+  }
+
+  return count
+}
+
+export { countSubstrings }
diff --git a/String/test/CountSubstrings.test.js b/String/test/CountSubstrings.test.js
new file mode 100644
index 0000000000..66628b1a14
--- /dev/null
+++ b/String/test/CountSubstrings.test.js
@@ -0,0 +1,52 @@
+import { countSubstrings } from '../CountSubstrings'
+
+describe('CountSubstrings', () => {
+  it('count multiple occurrences of substring in a string', () => {
+    const str = 'This is a string'
+    const substring = 'is'
+    const count = countSubstrings(str, substring)
+    expect(count).toBe(2)
+  })
+
+  it('should return 0 when input substring has no occurrences', () => {
+    const str = 'Jurassic Park'
+    const substring = 'World'
+    const count = countSubstrings(str, substring)
+    expect(count).toBe(0)
+  })
+
+  it('should return 1 when input substring is of length 1 that is equal to string', () => {
+    const str = 's'
+    const substring = 's'
+    const count = countSubstrings(str, substring)
+    expect(count).toBe(1)
+  })
+
+  it('should return the correct result when input string contains spaces', () => {
+    const str = 'ab cd ef  ghi'
+    const substring = ' '
+    const count = countSubstrings(str, substring)
+    expect(count).toBe(4)
+  })
+
+  it('should return the correct result when input substring contains number or special characters', () => {
+    const str = 'abc1@2def1@2'
+    const substring = '1@2'
+    const count = countSubstrings(str, substring)
+    expect(count).toBe(2)
+  })
+
+  it('should return string.length + 1 when the input substring is an empty string', () => {
+    const str = 'empty'
+    const substring = ''
+    const count = countSubstrings(str, substring)
+    expect(count).toBe(6)
+  })
+
+  it('should return correct result when input is overlapping substring', () => {
+    const str = 'aaa'
+    const substring = 'aa'
+    const count = countSubstrings(str, substring)
+    expect(count).toBe(2)
+  })
+})