diff --git a/types/chai-datetime/chai-datetime-tests.ts b/types/chai-datetime/chai-datetime-tests.ts
index 255d816b5a..f955e78e27 100644
--- a/types/chai-datetime/chai-datetime-tests.ts
+++ b/types/chai-datetime/chai-datetime-tests.ts
@@ -3,47 +3,65 @@ import chai = require('chai');
 import chaiDateTime = require('chai-datetime');
 
 chai.use(chaiDateTime);
-var expect = chai.expect;
-var assert = chai.assert;
+const expect = chai.expect;
+const assert = chai.assert;
 
 function test_equalTime(){
-    var date: Date = new Date(2014, 1, 1);
+    const date: Date = new Date(2014, 1, 1);
     expect(date).to.equalTime(date);
     date.should.equalTime(date);
     assert.equalTime(date, date);
 }
 
 function test_beforeTime(){
-    var date: Date = new Date(2014, 1, 1);
+    const date: Date = new Date(2014, 1, 1);
     expect(date).to.be.beforeTime(date);
     date.should.be.beforeTime(date);
     assert.beforeTime(date, date);
 }
 
 function test_afterTime(){
-    var date: Date = new Date(2014, 1, 1);
+    const date: Date = new Date(2014, 1, 1);
     expect(date).to.be.afterTime(date);
     date.should.be.afterTime(date);
     assert.afterTime(date, date);
 }
 
+function test_withinTime(){
+    const date: Date = new Date(2014, 7, 1);
+    const fromDate: Date = new Date(2014, 1, 1);
+    const toDate: Date = new Date(2015, 1, 1);
+    expect(date).to.be.withinTime(fromDate, toDate);
+    date.should.be.withinTime(fromDate, toDate);
+    assert.withinTime(date, fromDate, toDate);
+}
+
 function test_equalDate(){
-    var date: Date = new Date(2014, 1, 1);
+    const date: Date = new Date(2014, 1, 1);
     expect(date).to.equalDate(date);
     date.should.equalDate(date);
     assert.equalDate(date, date);
 }
 
 function test_beforeDate(){
-    var date: Date = new Date(2014, 1, 1);
+    const date: Date = new Date(2014, 1, 1);
     expect(date).to.be.beforeDate(date);
     date.should.be.beforeDate(date);
     assert.beforeDate(date, date);
 }
 
 function test_afterDate(){
-    var date: Date = new Date(2014, 1, 1);
+    const date: Date = new Date(2014, 1, 1);
     expect(date).to.be.afterDate(date);
     date.should.be.afterDate(date);
     assert.afterDate(date, date);
 }
+
+function test_withinDate(){
+    const date: Date = new Date(2014, 7, 1);
+    const fromDate: Date = new Date(2014, 1, 1);
+    const toDate: Date = new Date(2015, 1, 1);
+    expect(date).to.be.withinDate(fromDate, toDate);
+    date.should.be.withinDate(fromDate, toDate);
+    assert.withinDate(date, fromDate, toDate);
+}
diff --git a/types/chai-datetime/index.d.ts b/types/chai-datetime/index.d.ts
index 176d112dc0..be623a05d4 100644
--- a/types/chai-datetime/index.d.ts
+++ b/types/chai-datetime/index.d.ts
@@ -1,6 +1,7 @@
 // Type definitions for chai-datetime
 // Project: https://github.com/gaslight/chai-datetime.git
-// Definitions by: Cliff Burger <https://github.com/cliffburger>
+// Definitions by: Cliff Burger <https://github.com/cliffburger>,
+//                 Matt Bishop <https://github.com/mattbishop>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 
 /// <reference types="chai" />
@@ -14,9 +15,11 @@ declare global {
             afterDate(date: Date): Assertion;
             beforeDate(date: Date): Assertion;
             equalDate(date: Date): Assertion;
+            withinDate(dateFrom: Date, dateTo: Date): Assertion;
             afterTime(date: Date): Assertion;
             beforeTime(date: Date): Assertion;
             equalTime(date: Date): Assertion;
+            withinTime(dateFrom: Date, dateTo: Date): Assertion;
         }
 
         interface Assert {
@@ -26,12 +29,16 @@ declare global {
             notBeforeTime(val: Date, exp: Date, msg?: string): void;
             afterTime(val: Date, exp: Date, msg?: string): void;
             notAfterTime(val: Date, exp: Date, msg?: string): void;
+            withinTime(val: Date, expFrom: Date, expTo: Date, msg?: string): void;
+            notWithinTime(val: Date, expFrom: Date, expTo: Date, msg?: string): void;
             equalDate(val: Date, exp: Date, msg?: string): void;
             notEqualDate(val: Date, exp: Date, msg?: string): void;
             beforeDate(val: Date, exp: Date, msg?: string): void;
             notBeforeDate(val: Date, exp: Date, msg?: string): void;
             afterDate(val: Date, exp: Date, msg?: string): void;
             notAfterDate(val: Date, exp: Date, msg?: string): void;
+            withinDate(val: Date, expFrom: Date, expTo: Date, msg?: string): void;
+            notWithinDate(val: Date, expFrom: Date, expTo: Date, msg?: string): void;
         }
     }