diff --git a/src/main/java/edu/ntnu/idi/idatt/transaction/TransactionArchive.java b/src/main/java/edu/ntnu/idi/idatt/transaction/TransactionArchive.java
index 0567591..e07e8c9 100644
--- a/src/main/java/edu/ntnu/idi/idatt/transaction/TransactionArchive.java
+++ b/src/main/java/edu/ntnu/idi/idatt/transaction/TransactionArchive.java
@@ -73,8 +73,11 @@ public List<Sale> getSales(int week) {
    *
    * @return
    */
-  public int countDistinctWeeks() { // TODO: HERE
-    return -1;
+  public int countDistinctWeeks() {
+    return (int) transactions.stream()
+        .map(Transaction::getWeek)
+        .distinct()
+        .count();
   }
 
 }
diff --git a/src/test/java/edu/ntnu/idi/idatt/transaction/TransactionArchiveTest.java b/src/test/java/edu/ntnu/idi/idatt/transaction/TransactionArchiveTest.java
index 482a45c..74930fb 100644
--- a/src/test/java/edu/ntnu/idi/idatt/transaction/TransactionArchiveTest.java
+++ b/src/test/java/edu/ntnu/idi/idatt/transaction/TransactionArchiveTest.java
@@ -87,4 +87,18 @@ void PTgetTransactions() {
 
   }
 
+  /**
+   * Tests for countDistinctWeeks().
+   */
+  @Test
+  void PTcountDistinctWeeks() {
+    assertEquals(2, transactionArchive.countDistinctWeeks());
+  }
+
+  @Test
+  void NTcountDistinctWeeks() {
+    TransactionArchive tArchive = new TransactionArchive();
+    assertEquals(0, tArchive.countDistinctWeeks());
+  }
+
 }