diff --git a/lucene/core/src/java/org/apache/lucene/index/CachingMergeContext.java b/lucene/core/src/java/org/apache/lucene/index/CachingMergeContext.java
new file mode 100644
index 000000000000..9661ab91e76a
--- /dev/null
+++ b/lucene/core/src/java/org/apache/lucene/index/CachingMergeContext.java
@@ -0,0 +1,61 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.index;
+
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.Set;
+import org.apache.lucene.util.InfoStream;
+
+/**
+ * a wrapper of IndexWriter MergeContext. Try to cache the {@link
+ * #numDeletesToMerge(SegmentCommitInfo)} result in merge phase, to avoid duplicate calculation
+ */
+public class CachingMergeContext implements MergePolicy.MergeContext {
+  final MergePolicy.MergeContext mergeContext;
+  final HashMap<SegmentCommitInfo, Integer> cachedNumDeletesToMerge = new HashMap<>();
+
+  CachingMergeContext(MergePolicy.MergeContext mergeContext) {
+    this.mergeContext = mergeContext;
+  }
+
+  @Override
+  public final int numDeletesToMerge(SegmentCommitInfo info) throws IOException {
+    Integer numDeletesToMerge = cachedNumDeletesToMerge.get(info);
+    if (numDeletesToMerge != null) {
+      return numDeletesToMerge;
+    }
+    numDeletesToMerge = mergeContext.numDeletesToMerge(info);
+    cachedNumDeletesToMerge.put(info, numDeletesToMerge);
+    return numDeletesToMerge;
+  }
+
+  @Override
+  public final int numDeletedDocs(SegmentCommitInfo info) {
+    return mergeContext.numDeletedDocs(info);
+  }
+
+  @Override
+  public final InfoStream getInfoStream() {
+    return mergeContext.getInfoStream();
+  }
+
+  @Override
+  public final Set<SegmentCommitInfo> getMergingSegments() {
+    return mergeContext.getMergingSegments();
+  }
+}
diff --git a/lucene/core/src/java/org/apache/lucene/index/IndexWriter.java b/lucene/core/src/java/org/apache/lucene/index/IndexWriter.java
index 33cec219fac2..b562f7740d29 100644
--- a/lucene/core/src/java/org/apache/lucene/index/IndexWriter.java
+++ b/lucene/core/src/java/org/apache/lucene/index/IndexWriter.java
@@ -2214,10 +2214,11 @@ public void forceMergeDeletes(boolean doWait) throws IOException {
     }
 
     final MergePolicy mergePolicy = config.getMergePolicy();
+    final CachingMergeContext cachingMergeContext = new CachingMergeContext(this);
     MergePolicy.MergeSpecification spec;
     boolean newMergesFound = false;
     synchronized (this) {
-      spec = mergePolicy.findForcedDeletesMerges(segmentInfos, this);
+      spec = mergePolicy.findForcedDeletesMerges(segmentInfos, cachingMergeContext);
       newMergesFound = spec != null;
       if (newMergesFound) {
         final int numMerges = spec.merges.size();
@@ -2327,6 +2328,7 @@ private synchronized MergePolicy.MergeSpecification updatePendingMerges(
     }
 
     final MergePolicy.MergeSpecification spec;
+    final CachingMergeContext cachingMergeContext = new CachingMergeContext(this);
     if (maxNumSegments != UNBOUNDED_MAX_MERGE_SEGMENTS) {
       assert trigger == MergeTrigger.EXPLICIT || trigger == MergeTrigger.MERGE_FINISHED
           : "Expected EXPLICT or MERGE_FINISHED as trigger even with maxNumSegments set but was: "
@@ -2334,7 +2336,10 @@ private synchronized MergePolicy.MergeSpecification updatePendingMerges(
 
       spec =
           mergePolicy.findForcedMerges(
-              segmentInfos, maxNumSegments, Collections.unmodifiableMap(segmentsToMerge), this);
+              segmentInfos,
+              maxNumSegments,
+              Collections.unmodifiableMap(segmentsToMerge),
+              cachingMergeContext);
       if (spec != null) {
         final int numMerges = spec.merges.size();
         for (int i = 0; i < numMerges; i++) {
@@ -2346,7 +2351,7 @@ private synchronized MergePolicy.MergeSpecification updatePendingMerges(
       switch (trigger) {
         case GET_READER:
         case COMMIT:
-          spec = mergePolicy.findFullFlushMerges(trigger, segmentInfos, this);
+          spec = mergePolicy.findFullFlushMerges(trigger, segmentInfos, cachingMergeContext);
           break;
         case ADD_INDEXES:
           throw new IllegalStateException(
@@ -2358,7 +2363,7 @@ private synchronized MergePolicy.MergeSpecification updatePendingMerges(
         case SEGMENT_FLUSH:
         case CLOSING:
         default:
-          spec = mergePolicy.findMerges(trigger, segmentInfos, this);
+          spec = mergePolicy.findMerges(trigger, segmentInfos, cachingMergeContext);
       }
     }
     if (spec != null) {