diff --git a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/score/DecayTests.java b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/score/DecayTests.java
index c51f595ab95ce..34d05e66ad0b4 100644
--- a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/score/DecayTests.java
+++ b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/score/DecayTests.java
@@ -20,6 +20,7 @@
 import org.elasticsearch.xpack.esql.core.type.DataType;
 import org.elasticsearch.xpack.esql.expression.function.AbstractScalarFunctionTestCase;
 import org.elasticsearch.xpack.esql.expression.function.TestCaseSupplier;
+import org.elasticsearch.xpack.esql.expression.function.scalar.score.Decay.DecayFunction;
 import org.hamcrest.Matcher;
 
 import java.math.BigDecimal;
@@ -638,9 +639,10 @@ private static List<TestCaseSupplier> intRandomTestCases() {
         return List.of(new TestCaseSupplier(List.of(DataType.INTEGER, DataType.INTEGER, DataType.INTEGER, DataType.SOURCE), () -> {
             int randomValue = randomInt();
             int randomOrigin = randomInt();
-            int randomScale = randomInt();
+            // scale must be > 0
+            int randomScale = randomIntBetween(1, Integer.MAX_VALUE);
             int randomOffset = randomInt();
-            double randomDecay = randomDouble();
+            double randomDecay = randomDecayOpenUnitInterval();
             String randomType = getRandomType();
 
             double scoreScriptNumericResult = intDecayWithScoreScript(
@@ -712,9 +714,9 @@ private static List<TestCaseSupplier> longRandomTestCases() {
         return List.of(new TestCaseSupplier(List.of(DataType.LONG, DataType.LONG, DataType.LONG, DataType.SOURCE), () -> {
             long randomValue = randomLong();
             long randomOrigin = randomLong();
-            long randomScale = randomLong();
+            long randomScale = randomLongBetween(1L, Long.MAX_VALUE);
             long randomOffset = randomLong();
-            double randomDecay = randomDouble();
+            double randomDecay = randomDecayOpenUnitInterval();
             String randomType = randomFrom("linear", "gauss", "exp");
 
             double scoreScriptNumericResult = longDecayWithScoreScript(
@@ -782,9 +784,9 @@ private static List<TestCaseSupplier> doubleRandomTestCases() {
         return List.of(new TestCaseSupplier(List.of(DataType.DOUBLE, DataType.DOUBLE, DataType.DOUBLE, DataType.SOURCE), () -> {
             double randomValue = randomLong();
             double randomOrigin = randomLong();
-            double randomScale = randomLong();
+            double randomScale = randomLongBetween(1L, Long.MAX_VALUE);
             double randomOffset = randomLong();
-            double randomDecay = randomDouble();
+            double randomDecay = randomDecayOpenUnitInterval();
             String randomType = randomFrom("linear", "gauss", "exp");
 
             double scoreScriptNumericResult = doubleDecayWithScoreScript(
@@ -882,7 +884,7 @@ private static List<TestCaseSupplier> geoPointRandomTestCases() {
             GeoPoint randomOrigin = randomGeoPoint();
             String randomScale = randomDistance();
             String randomOffset = randomDistance();
-            double randomDecay = randomDouble();
+            double randomDecay = randomDecayOpenUnitInterval();
             String randomType = randomDecayType();
 
             double scoreScriptNumericResult = geoPointDecayWithScoreScript(
@@ -1061,7 +1063,7 @@ private static List<TestCaseSupplier> datetimeRandomTestCases() {
             long randomOffsetMillis = randomNonNegativeLong() % (30L * 24 * 60 * 60 * 1000);
             Duration randomScale = Duration.ofMillis(randomScaleMillis);
             Duration randomOffset = Duration.ofMillis(randomOffsetMillis);
-            double randomDecay = randomDouble();
+            double randomDecay = randomDecayOpenUnitInterval();
             String randomType = randomFrom("linear", "gauss", "exp");
 
             double scoreScriptNumericResult = datetimeDecayWithScoreScript(
@@ -1148,14 +1150,14 @@ private static List<TestCaseSupplier> dateNanosRandomTestCases() {
                 Duration randomScale = Duration.ofMillis(randomScaleMillis);
                 Duration randomOffset = Duration.ofMillis(randomOffsetMillis);
 
-                double randomDecay = randomDouble();
+                double randomDecay = randomDecayOpenUnitInterval();
                 String randomType = randomFrom("linear", "gauss", "exp");
 
-                double scoreScriptNumericResult = dateNanosDecayWithScoreScript(
+                double scoreScriptNumericResult = expectedDateNanosTemporalDecay(
                     randomValue,
                     randomOrigin,
-                    randomScale.toMillis(),
-                    randomOffset.toMillis(),
+                    randomScale.toNanos(),
+                    randomOffset.toNanos(),
                     randomDecay,
                     randomType
                 );
@@ -1176,24 +1178,30 @@ private static List<TestCaseSupplier> dateNanosRandomTestCases() {
         );
     }
 
-    private static double dateNanosDecayWithScoreScript(long value, long origin, long scale, long offset, double decay, String type) {
-        long valueMillis = value / 1_000_000L;
-        long originMillis = origin / 1_000_000L;
-
-        String originStr = String.valueOf(originMillis);
-        String scaleStr = scale + "ms";
-        String offsetStr = offset + "ms";
-
-        ZonedDateTime valueDateTime = Instant.ofEpochMilli(valueMillis).atZone(ZoneId.of("UTC"));
+    private static double expectedDateNanosTemporalDecay(
+        long valueNanos,
+        long originNanos,
+        long scaleNanos,
+        long offsetNanos,
+        double decay,
+        String type
+    ) {
+        return decayFunctionForType(type).temporalDecay(valueNanos, originNanos, scaleNanos, offsetNanos, decay);
+    }
 
+    private static DecayFunction decayFunctionForType(String type) {
         return switch (type) {
-            case "linear" -> new ScoreScriptUtils.DecayDateLinear(originStr, scaleStr, offsetStr, decay).decayDateLinear(valueDateTime);
-            case "gauss" -> new ScoreScriptUtils.DecayDateGauss(originStr, scaleStr, offsetStr, decay).decayDateGauss(valueDateTime);
-            case "exp" -> new ScoreScriptUtils.DecayDateExp(originStr, scaleStr, offsetStr, decay).decayDateExp(valueDateTime);
+            case "linear" -> DecayFunction.LINEAR;
+            case "gauss" -> DecayFunction.GAUSSIAN;
+            case "exp" -> DecayFunction.EXPONENTIAL;
             default -> throw new IllegalArgumentException("Unknown decay function type [" + type + "]");
         };
     }
 
+    private static double randomDecayOpenUnitInterval() {
+        return randomDoubleBetween(1e-12, Math.nextDown(1.0), true);
+    }
+
     private static MapExpression createOptionsMap(Object offset, Double decay, String functionType) {
         List<Expression> keyValuePairs = new ArrayList<>();