diff --git a/Plan/src/main/java/com/djrapitops/plan/data/store/mutators/TPSMutator.java b/Plan/src/main/java/com/djrapitops/plan/data/store/mutators/TPSMutator.java
index 302d8e914..8af6fa550 100644
--- a/Plan/src/main/java/com/djrapitops/plan/data/store/mutators/TPSMutator.java
+++ b/Plan/src/main/java/com/djrapitops/plan/data/store/mutators/TPSMutator.java
@@ -4,6 +4,7 @@ import com.djrapitops.plan.data.container.TPS;
 import com.djrapitops.plan.data.store.containers.DataContainer;
 import com.djrapitops.plan.data.store.keys.ServerKeys;
 import com.djrapitops.plan.system.settings.Settings;
+import com.djrapitops.plan.utilities.comparators.TPSComparator;
 import com.djrapitops.plan.utilities.html.graphs.line.Point;
 import com.djrapitops.plugin.api.TimeAmount;
 
@@ -89,6 +90,7 @@ public class TPSMutator {
     public long serverDownTime() {
         long lastDate = -1;
         long downTime = 0;
+        tpsData.sort(new TPSComparator());
         for (TPS tps : tpsData) {
             long date = tps.getDate();
             if (lastDate == -1) {
@@ -110,6 +112,7 @@ public class TPSMutator {
         long lastDate = -1;
         int lastPlayers = 0;
         long idleTime = 0;
+        tpsData.sort(new TPSComparator());
         for (TPS tps : tpsData) {
             long date = tps.getDate();
             int players = tps.getPlayers();
diff --git a/Plan/src/test/java/com/djrapitops/plan/data/store/mutators/TPSMutatorTest.java b/Plan/src/test/java/com/djrapitops/plan/data/store/mutators/TPSMutatorTest.java
new file mode 100644
index 000000000..33d93c5e8
--- /dev/null
+++ b/Plan/src/test/java/com/djrapitops/plan/data/store/mutators/TPSMutatorTest.java
@@ -0,0 +1,138 @@
+package com.djrapitops.plan.data.store.mutators;
+
+import com.djrapitops.plan.data.container.TPS;
+import com.djrapitops.plan.data.container.builders.TPSBuilder;
+import com.djrapitops.plugin.api.TimeAmount;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import static org.junit.Assert.*;
+
+/**
+ * Tests for {@link TPSMutator}
+ *
+ * @author Rsl1122
+ */
+public class TPSMutatorTest {
+
+    private List<TPS> testData;
+    private long time;
+
+    @Before
+    public void setUp() {
+        testData = new ArrayList<>();
+
+        time = System.currentTimeMillis();
+        long twoMonthsAgo = time - TimeAmount.MONTH.ms() * 2L;
+
+        for (long date = twoMonthsAgo; date < time; date += TimeAmount.MINUTE.ms()) {
+            testData.add(
+                    TPSBuilder.get().date(date)
+                            .tps(0.0)
+                            .playersOnline(0)
+                            .usedCPU(0.0)
+                            .usedMemory(0)
+                            .entities(0)
+                            .chunksLoaded(0)
+                            .toTPS()
+            );
+        }
+    }
+
+    @Test
+    public void noDownTimeIsCorrect() {
+        long expected = 0;
+        long result = new TPSMutator(testData).serverDownTime();
+        assertEquals(expected, result);
+    }
+
+    @Test
+    public void noDownTimeOnSingleEntry() {
+        long expected = 0;
+        long result = new TPSMutator(Collections.singletonList(
+                TPSBuilder.get().date(time - TimeAmount.DAY.ms())
+                        .tps(0.0)
+                        .playersOnline(0)
+                        .usedCPU(0.0)
+                        .usedMemory(0)
+                        .entities(0)
+                        .chunksLoaded(0)
+                        .toTPS()
+        )).serverDownTime();
+        assertEquals(expected, result);
+    }
+
+    @Test
+    public void fullDownTime() {
+        long periodLength = TimeAmount.MINUTE.ms() * 5L;
+        long expected = TimeAmount.MONTH.ms() * 2L - periodLength;
+
+        TPSMutator tpsMutator = new TPSMutator(testData.stream()
+                .filter(tps -> (tps.getDate() - time) % (periodLength) == 0)
+                .collect(Collectors.toList()));
+        assertFalse(tpsMutator.all().isEmpty());
+        assertNotEquals(testData, tpsMutator.all());
+
+        long result = tpsMutator.serverDownTime();
+        assertEquals(expected, result);
+    }
+
+    @Test
+    public void filteredFullMonthDownTime() {
+        long periodLength = TimeAmount.MINUTE.ms() * 5L;
+        long expected = TimeAmount.MONTH.ms() - periodLength;
+
+        long monthAgo = time - TimeAmount.MONTH.ms();
+        TPSMutator tpsMutator = new TPSMutator(testData.stream()
+                .filter(tps -> (tps.getDate() - time) % (periodLength) == 0)
+                .collect(Collectors.toList()))
+                .filterDataBetween(monthAgo, time);
+
+        assertFalse(tpsMutator.all().isEmpty());
+        assertNotEquals(testData, tpsMutator.filterDataBetween(monthAgo, time).all());
+
+        long result = tpsMutator.serverDownTime();
+        assertEquals(expected, result);
+    }
+
+    @Test
+    public void filteredFullMonthDownTimeWhenRandomOrder() {
+        long periodLength = TimeAmount.MINUTE.ms() * 5L;
+        long expected = TimeAmount.MONTH.ms() - periodLength;
+
+        List<TPS> randomOrder = testData;
+        Collections.shuffle(randomOrder);
+        long monthAgo = time - TimeAmount.MONTH.ms();
+        TPSMutator tpsMutator = new TPSMutator(randomOrder.stream()
+                .filter(tps -> (tps.getDate() - time) % (periodLength) == 0)
+                .collect(Collectors.toList()))
+                .filterDataBetween(monthAgo, time);
+
+        assertFalse(tpsMutator.all().isEmpty());
+        assertNotEquals(randomOrder, tpsMutator.filterDataBetween(monthAgo, time).all());
+
+        long result = tpsMutator.serverDownTime();
+        assertEquals(expected, result);
+    }
+
+    @Test
+    public void filterWorksCorrectly() {
+        long monthAgo = time - TimeAmount.MONTH.ms();
+        List<TPS> filtered = new TPSMutator(testData).filterDataBetween(monthAgo, time).all();
+
+        for (TPS tps : filtered) {
+            long date = tps.getDate();
+            if (date < monthAgo) {
+                fail("Data from over month ago was present");
+            }
+            if (date > time) {
+                fail("Data from after 'time' was present");
+            }
+        }
+    }
+}
\ No newline at end of file