diff --git a/poi/src/main/java/org/apache/poi/ss/formula/atp/AnalysisToolPak.java b/poi/src/main/java/org/apache/poi/ss/formula/atp/AnalysisToolPak.java
index 1482a39197..bf92661089 100644
--- a/poi/src/main/java/org/apache/poi/ss/formula/atp/AnalysisToolPak.java
+++ b/poi/src/main/java/org/apache/poi/ss/formula/atp/AnalysisToolPak.java
@@ -112,6 +112,7 @@ public final class AnalysisToolPak implements UDFFinder {
         r(m, "ERF", null);
         r(m, "ERFC", null);
         r(m, "FACTDOUBLE", FactDouble.instance);
+        r(m, "FLOOR.MATH", FloorMath.instance);
         r(m, "FVSCHEDULE", null);
         r(m, "GCD", Gcd.instance);
         r(m, "GESTEP", null);
diff --git a/poi/src/main/java/org/apache/poi/ss/formula/functions/CeilingMath.java b/poi/src/main/java/org/apache/poi/ss/formula/functions/CeilingMath.java
index 8ca82f7c2e..6c84abfea0 100644
--- a/poi/src/main/java/org/apache/poi/ss/formula/functions/CeilingMath.java
+++ b/poi/src/main/java/org/apache/poi/ss/formula/functions/CeilingMath.java
@@ -24,9 +24,10 @@ import org.apache.poi.ss.formula.eval.NumberEval;
 import org.apache.poi.ss.formula.eval.OperandResolver;
 import org.apache.poi.ss.formula.eval.ValueEval;
 
-import java.math.BigDecimal;
 import java.math.RoundingMode;
 
+import static org.apache.poi.ss.formula.functions.MathX.scaledRoundUsingBigDecimal;
+
 /**
  * Implementation for Excel CEILING.MATH() function.
  * <ul>
@@ -61,12 +62,12 @@ public final class CeilingMath implements FreeRefFunction {
             }
             if (roundNegativeNumsDown && xval < 0.0) {
                 if (multiplier != 1.0) {
-                    return new NumberEval(roundUsingBigDecimal(xval, multiplier, RoundingMode.FLOOR));
+                    return new NumberEval(scaledRoundUsingBigDecimal(xval, multiplier, RoundingMode.FLOOR));
                 }
                 return new NumberEval(Math.floor(xval));
             }
             if (multiplier != 1.0) {
-                return new NumberEval(roundUsingBigDecimal(xval, multiplier, RoundingMode.CEILING));
+                return new NumberEval(scaledRoundUsingBigDecimal(xval, multiplier, RoundingMode.CEILING));
             }
             return new NumberEval(Math.ceil(xval));
         } catch (EvaluationException evaluationException) {
@@ -74,14 +75,6 @@ public final class CeilingMath implements FreeRefFunction {
         }
     }
 
-    private double roundUsingBigDecimal(double xval, double multiplier, RoundingMode mode) {
-        BigDecimal multiplierDecimal = BigDecimal.valueOf(multiplier);
-        BigDecimal bd = BigDecimal.valueOf(xval).divide(multiplierDecimal)
-                .setScale(0, mode)
-                .multiply(multiplierDecimal);
-        return bd.doubleValue();
-    }
-
     private static Double evaluateValue(ValueEval arg, int srcRowIndex, int srcColumnIndex) throws EvaluationException {
         ValueEval veText = OperandResolver.getSingleValue(arg, srcRowIndex, srcColumnIndex);
         String strText1 = OperandResolver.coerceValueToString(veText);
diff --git a/poi/src/main/java/org/apache/poi/ss/formula/functions/FloorMath.java b/poi/src/main/java/org/apache/poi/ss/formula/functions/FloorMath.java
new file mode 100644
index 0000000000..0b0d13928b
--- /dev/null
+++ b/poi/src/main/java/org/apache/poi/ss/formula/functions/FloorMath.java
@@ -0,0 +1,83 @@
+/* ====================================================================
+   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.poi.ss.formula.functions;
+
+import org.apache.poi.ss.formula.OperationEvaluationContext;
+import org.apache.poi.ss.formula.eval.ErrorEval;
+import org.apache.poi.ss.formula.eval.EvaluationException;
+import org.apache.poi.ss.formula.eval.NumberEval;
+import org.apache.poi.ss.formula.eval.OperandResolver;
+import org.apache.poi.ss.formula.eval.ValueEval;
+
+import java.math.RoundingMode;
+
+import static org.apache.poi.ss.formula.functions.MathX.scaledRoundUsingBigDecimal;
+
+/**
+ * Implementation for Excel FLOOR.MATH() function.
+ * <ul>
+ *   <li>https://support.microsoft.com/en-us/office/floor-math-function-c302b599-fbdb-4177-ba19-2c2b1249a2f5</li>
+ * </ul>
+ */
+public final class FloorMath implements FreeRefFunction {
+
+    public static final FloorMath instance = new FloorMath();
+
+    private FloorMath() {}
+
+    @Override
+    public ValueEval evaluate(ValueEval[] args, OperationEvaluationContext ec) {
+        if (args.length == 0) {
+            return ErrorEval.VALUE_INVALID;
+        }
+        try {
+            Double xval = evaluateValue(args[0], ec.getRowIndex(), ec.getColumnIndex());
+            if (xval == null) {
+                return ErrorEval.NUM_ERROR;
+            }
+            double multiplier = 1.0;
+            if (args.length > 1) {
+                Double arg1Val = evaluateValue(args[1], ec.getRowIndex(), ec.getColumnIndex());
+                multiplier = arg1Val != null ? arg1Val.doubleValue() : 1.0;
+            }
+            boolean roundNegativeNumsDown = false;
+            if (args.length > 2) {
+                Double arg2Val = evaluateValue(args[2], ec.getRowIndex(), ec.getColumnIndex());
+                roundNegativeNumsDown = arg2Val != null && arg2Val.doubleValue() < 0.0;
+            }
+            if (roundNegativeNumsDown && xval < 0.0) {
+                if (multiplier != 1.0) {
+                    return new NumberEval(scaledRoundUsingBigDecimal(xval, multiplier, RoundingMode.CEILING));
+                }
+                return new NumberEval(Math.ceil(xval));
+            }
+            if (multiplier != 1.0) {
+                return new NumberEval(scaledRoundUsingBigDecimal(xval, multiplier, RoundingMode.FLOOR));
+            }
+            return new NumberEval(Math.floor(xval));
+        } catch (EvaluationException evaluationException) {
+            return evaluationException.getErrorEval();
+        }
+    }
+
+    private static Double evaluateValue(ValueEval arg, int srcRowIndex, int srcColumnIndex) throws EvaluationException {
+        ValueEval veText = OperandResolver.getSingleValue(arg, srcRowIndex, srcColumnIndex);
+        String strText1 = OperandResolver.coerceValueToString(veText);
+        return OperandResolver.parseDouble(strText1);
+    }
+}
\ No newline at end of file
diff --git a/poi/src/main/java/org/apache/poi/ss/formula/functions/MathX.java b/poi/src/main/java/org/apache/poi/ss/formula/functions/MathX.java
index 387a4e8397..3efa5bc335 100644
--- a/poi/src/main/java/org/apache/poi/ss/formula/functions/MathX.java
+++ b/poi/src/main/java/org/apache/poi/ss/formula/functions/MathX.java
@@ -19,6 +19,9 @@ package org.apache.poi.ss.formula.functions;
 
 import org.apache.poi.ss.util.NumberToTextConverter;
 
+import java.math.BigDecimal;
+import java.math.RoundingMode;
+
 /**
  * This class is an extension to the standard math library
  * provided by java.lang.Math class. It follows the Math class
@@ -231,7 +234,13 @@ final class MathX {
         if (s==0 && n!=0) {
             return Double.NaN;
         } else {
-            return (n==0 || s==0) ? 0 : Math.floor(n/s) * s;
+            if (n == 0.0 || s == 0.0) {
+                return 0.0;
+            } else if (s == 1.0) {
+                return Math.floor(n);
+            } else {
+                return scaledRoundUsingBigDecimal(n, s, RoundingMode.FLOOR);
+            }
         }
     }
 
@@ -254,10 +263,24 @@ final class MathX {
         if (n>0 && s<0) {
             return Double.NaN;
         } else {
-            return (n == 0 || s == 0) ? 0 : Math.ceil(n/s) * s;
+            if (n == 0.0 || s == 0.0) {
+                return 0.0;
+            } else if (s == 1.0) {
+                return Math.ceil(n);
+            } else {
+                return scaledRoundUsingBigDecimal(n, s, RoundingMode.CEILING);
+            }
         }
     }
 
+    public static double scaledRoundUsingBigDecimal(double xval, double multiplier, RoundingMode mode) {
+        BigDecimal multiplierDecimal = BigDecimal.valueOf(multiplier);
+        BigDecimal bd = BigDecimal.valueOf(xval).divide(multiplierDecimal)
+                .setScale(0, mode)
+                .multiply(multiplierDecimal);
+        return bd.doubleValue();
+    }
+
     /**
      * <br> for all n >= 1; factorial n = n * (n-1) * (n-2) * ... * 1
      * <br> else if n == 0; factorial n = 1
diff --git a/poi/src/test/java/org/apache/poi/ss/formula/functions/TestCeilingMath.java b/poi/src/test/java/org/apache/poi/ss/formula/functions/TestCeilingMath.java
index a80ea8e45e..5780f58562 100644
--- a/poi/src/test/java/org/apache/poi/ss/formula/functions/TestCeilingMath.java
+++ b/poi/src/test/java/org/apache/poi/ss/formula/functions/TestCeilingMath.java
@@ -22,8 +22,6 @@ import org.apache.poi.hssf.usermodel.HSSFFormulaEvaluator;
 import org.apache.poi.hssf.usermodel.HSSFRow;
 import org.apache.poi.hssf.usermodel.HSSFSheet;
 import org.apache.poi.hssf.usermodel.HSSFWorkbook;
-import org.apache.poi.ss.formula.OperationEvaluationContext;
-import org.apache.poi.ss.formula.eval.ErrorEval;
 import org.apache.poi.ss.usermodel.FormulaError;
 import org.junit.jupiter.api.Test;
 
@@ -37,8 +35,6 @@ import static org.apache.poi.ss.util.Utils.assertError;
  */
 final class TestCeilingMath {
 
-    private static final OperationEvaluationContext ec = new OperationEvaluationContext(null, null, 0, 0, 0, null);
-
     //https://support.microsoft.com/en-us/office/ceiling-math-function-80f95d2f-b499-4eee-9f16-f795a8e306c8
     @Test
     void testMicrosoftExamples() throws IOException {
diff --git a/poi/src/test/java/org/apache/poi/ss/formula/functions/TestFloorMath.java b/poi/src/test/java/org/apache/poi/ss/formula/functions/TestFloorMath.java
new file mode 100644
index 0000000000..b171261969
--- /dev/null
+++ b/poi/src/test/java/org/apache/poi/ss/formula/functions/TestFloorMath.java
@@ -0,0 +1,74 @@
+/* ====================================================================
+   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.poi.ss.formula.functions;
+
+import org.apache.poi.hssf.usermodel.HSSFCell;
+import org.apache.poi.hssf.usermodel.HSSFFormulaEvaluator;
+import org.apache.poi.hssf.usermodel.HSSFRow;
+import org.apache.poi.hssf.usermodel.HSSFSheet;
+import org.apache.poi.hssf.usermodel.HSSFWorkbook;
+import org.apache.poi.ss.usermodel.FormulaError;
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+
+import static org.apache.poi.ss.util.Utils.assertDouble;
+import static org.apache.poi.ss.util.Utils.assertError;
+
+/**
+ * Tests for {@link FloorMath}
+ */
+final class TestFloorMath {
+
+    //https://support.microsoft.com/en-us/office/floor-math-function-c302b599-fbdb-4177-ba19-2c2b1249a2f5
+    @Test
+    void testMicrosoftExamples() throws IOException {
+        try (HSSFWorkbook wb = new HSSFWorkbook()) {
+            HSSFSheet sheet = wb.createSheet();
+            HSSFRow row = sheet.createRow(0);
+            HSSFCell cell = row.createCell(0);
+            HSSFFormulaEvaluator fe = new HSSFFormulaEvaluator(wb);
+            assertDouble(fe, cell, "FLOOR.MATH(24.3,5)", 20.0, 0.00000000000001);
+            assertDouble(fe, cell, "FLOOR.MATH(6.7)", 6.0, 0.00000000000001);
+            assertDouble(fe, cell, "FLOOR.MATH(-8.1,2)", -10.0, 0.00000000000001);
+            assertDouble(fe, cell, "FLOOR.MATH(-5.5,2,-1)", -4.0, 0.00000000000001);
+        }
+    }
+
+    @Test
+    void testInvalid() throws IOException {
+        try (HSSFWorkbook wb = new HSSFWorkbook()) {
+            HSSFSheet sheet = wb.createSheet();
+            HSSFRow row = sheet.createRow(0);
+            HSSFCell cell = row.createCell(0);
+            HSSFFormulaEvaluator fe = new HSSFFormulaEvaluator(wb);
+            assertError(fe, cell, "FLOOR.MATH()", FormulaError.VALUE);
+        }
+    }
+
+    @Test
+    void testNumError() throws IOException {
+        try (HSSFWorkbook wb = new HSSFWorkbook()) {
+            HSSFSheet sheet = wb.createSheet();
+            HSSFRow row = sheet.createRow(0);
+            HSSFCell cell = row.createCell(0);
+            HSSFFormulaEvaluator fe = new HSSFFormulaEvaluator(wb);
+            assertError(fe, cell, "FLOOR.MATH(\"abc\")", FormulaError.NUM);
+        }
+    }
+}