diff --git a/fs_mgr/libdm/dm_target.cpp b/fs_mgr/libdm/dm_target.cpp
index 1a483ec..9152677 100644
--- a/fs_mgr/libdm/dm_target.cpp
+++ b/fs_mgr/libdm/dm_target.cpp
@@ -150,6 +150,25 @@
     return base_device_ + " " + cow_device_ + " " + mode + " " + std::to_string(chunk_size_);
 }
 
+// Computes the percentage of complition for snapshot status.
+// @sectors_initial is the number of sectors_allocated stored right before
+// starting the merge.
+double DmTargetSnapshot::MergePercent(const DmTargetSnapshot::Status& status,
+                                      uint64_t sectors_initial) {
+    uint64_t s = status.sectors_allocated;
+    uint64_t t = status.total_sectors;
+    uint64_t m = status.metadata_sectors;
+    uint64_t i = sectors_initial == 0 ? t : sectors_initial;
+
+    if (t <= s || i <= s) {
+        return 0.0;
+    }
+    if (s == 0 || t == 0 || s <= m) {
+        return 100.0;
+    }
+    return 100.0 / (i - m) * (i - s);
+}
+
 bool DmTargetSnapshot::ReportsOverflow(const std::string& target_type) {
     DeviceMapper& dm = DeviceMapper::Instance();
     DmTargetTypeInfo info;
diff --git a/fs_mgr/libdm/dm_test.cpp b/fs_mgr/libdm/dm_test.cpp
index 16be0d5..eed21dc 100644
--- a/fs_mgr/libdm/dm_test.cpp
+++ b/fs_mgr/libdm/dm_test.cpp
@@ -483,6 +483,60 @@
     EXPECT_TRUE(DmTargetSnapshot::ParseStatusText("Overflow", &status));
 }
 
+TEST(libdm, DmSnapshotMergePercent) {
+    DmTargetSnapshot::Status status;
+
+    // Correct input
+    status.sectors_allocated = 1000;
+    status.total_sectors = 1000;
+    status.metadata_sectors = 0;
+    EXPECT_LE(DmTargetSnapshot::MergePercent(status), 1.0);
+
+    status.sectors_allocated = 500;
+    status.total_sectors = 1000;
+    status.metadata_sectors = 0;
+    EXPECT_GE(DmTargetSnapshot::MergePercent(status), 49.0);
+    EXPECT_LE(DmTargetSnapshot::MergePercent(status), 51.0);
+
+    status.sectors_allocated = 0;
+    status.total_sectors = 1000;
+    status.metadata_sectors = 0;
+    EXPECT_GE(DmTargetSnapshot::MergePercent(status), 99.0);
+
+    status.sectors_allocated = 500;
+    status.total_sectors = 1000;
+    status.metadata_sectors = 500;
+    EXPECT_GE(DmTargetSnapshot::MergePercent(status), 99.0);
+
+    status.sectors_allocated = 500;
+    status.total_sectors = 1000;
+    status.metadata_sectors = 0;
+    EXPECT_LE(DmTargetSnapshot::MergePercent(status, 500), 1.0);
+    EXPECT_LE(DmTargetSnapshot::MergePercent(status, 1000), 51.0);
+    EXPECT_GE(DmTargetSnapshot::MergePercent(status, 1000), 49.0);
+
+    // Robustness
+    status.sectors_allocated = 2000;
+    status.total_sectors = 1000;
+    status.metadata_sectors = 0;
+    EXPECT_LE(DmTargetSnapshot::MergePercent(status), 0.0);
+
+    status.sectors_allocated = 2000;
+    status.total_sectors = 1000;
+    status.metadata_sectors = 2000;
+    EXPECT_LE(DmTargetSnapshot::MergePercent(status), 0.0);
+
+    status.sectors_allocated = 2000;
+    status.total_sectors = 0;
+    status.metadata_sectors = 2000;
+    EXPECT_LE(DmTargetSnapshot::MergePercent(status), 0.0);
+
+    status.sectors_allocated = 1000;
+    status.total_sectors = 0;
+    status.metadata_sectors = 1000;
+    EXPECT_LE(DmTargetSnapshot::MergePercent(status, 0), 0.0);
+}
+
 TEST(libdm, CryptArgs) {
     DmTargetCrypt target1(0, 512, "sha1", "abcdefgh", 50, "/dev/loop0", 100);
     ASSERT_EQ(target1.name(), "crypt");
diff --git a/fs_mgr/libdm/include/libdm/dm_target.h b/fs_mgr/libdm/include/libdm/dm_target.h
index 722922d..ab7c2db 100644
--- a/fs_mgr/libdm/include/libdm/dm_target.h
+++ b/fs_mgr/libdm/include/libdm/dm_target.h
@@ -216,6 +216,7 @@
         std::string error;
     };
 
+    static double MergePercent(const Status& status, uint64_t sectors_initial = 0);
     static bool ParseStatusText(const std::string& text, Status* status);
     static bool ReportsOverflow(const std::string& target_type);