diff --git a/src/helper/argParse.ts b/src/helper/argParse.ts
index 63bc148..b8e37e7 100644
--- a/src/helper/argParse.ts
+++ b/src/helper/argParse.ts
@@ -245,6 +245,11 @@ export const parsedArgs = y
       "How to bias where to place an operation during the scheduling mutation. 'reversebell' , 'uniform' uniformly selects in the possible interval.",
     choices: SPILLING,
   })
+  .option("threshold", {
+    default: 0,
+    number: true,
+    describe: "How likely is a worse solution to be accepted. -1 for auto, i.e. depening on how bad it is.",
+  })
   .help("help")
   .alias("h", "help")
   .wrap(Math.min(160, y.terminalWidth()))
diff --git a/src/optimizer/optimizer.class.ts b/src/optimizer/optimizer.class.ts
index 4dfbdea..8448c1f 100644
--- a/src/optimizer/optimizer.class.ts
+++ b/src/optimizer/optimizer.class.ts
@@ -41,7 +41,7 @@ import { RegisterAllocator } from "@/registerAllocator";
 import type { AnalyseResult, OptimizerArgs } from "@/types";
 
 import { genStatistics, genStatusLine, logMutation, printStartInfo } from "./optimizer.helper";
-import { init } from "./optimizer.helper.class";
+import { init, acceptWorseWithThres } from "./optimizer.helper.class";
 import MeasureUtil from "./measure.class";
 
 let choice: CHOICE;
@@ -285,10 +285,11 @@ export class Optimizer {
           let kept: boolean;
 
           if (
-            // A is not worse and A is new
-            (metricA <= metricB && currentFunctionIsA()) ||
-            // or B is not worse and B is new
-            (metricA >= metricB && !currentFunctionIsA())
+            acceptWorseWithThres(
+              currentFunctionIsA() ? metricA : metricB,
+              currentFunctionIsA() ? metricB : metricA,
+              this.args.threshold,
+            )
           ) {
             Logger.log("kept    mutation");
             kept = true;
diff --git a/src/optimizer/optimizer.helper.class.ts b/src/optimizer/optimizer.helper.class.ts
index 77ccc1a..fef7485 100644
--- a/src/optimizer/optimizer.helper.class.ts
+++ b/src/optimizer/optimizer.helper.class.ts
@@ -186,3 +186,18 @@ export function init(tmpDir: string, args: neededArgs): { symbolname: string; me
   }
   return createMS(r, sharedObjectFilename);
 }
+export function acceptWorseWithThres(new_metric: number, old_metric: number, thres: number): boolean {
+  // if the new one is already better, then accept
+  if (new_metric <= old_metric) {
+    return true;
+  }
+
+  // else acceptance depends on the threshold.
+  // -1 means auto
+  if (thres == -1) {
+    const relation = old_metric / new_metric; // 0<relation<1
+    return Math.random() <= 0.077426 * Math.exp(2.5584 * relation);
+  }
+  // else acceptance is constant and we accept with that probability
+  return Math.random() <= thres;
+}
diff --git a/src/types/optimizer.types.ts b/src/types/optimizer.types.ts
index 23b21f2..e1eb266 100644
--- a/src/types/optimizer.types.ts
+++ b/src/types/optimizer.types.ts
@@ -47,6 +47,7 @@ export type OptimizerArgs = {
   uicaarch: UICA_OPTIONS_T;
   objectiveFunction: OBJECTIVE_FUNCTION_OPTIONS_T;
   spilling: SPILLING_T;
+  threshold: number;
 };
 export type ParsedArgsT = OptimizerArgs & {
   startFromBestJson: boolean;
diff --git a/test/optimiser/optimiser.helper.class.ts b/test/optimiser/optimiser.helper.class.ts
new file mode 100644
index 0000000..fbc435c
--- /dev/null
+++ b/test/optimiser/optimiser.helper.class.ts
@@ -0,0 +1,73 @@
+/**
+ * Copyright 2023 University of Adelaide
+ *
+ * Licensed 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.
+ */
+
+import { afterAll, beforeAll, describe, expect, it, vi } from "vitest";
+
+import { acceptWorseWithThres } from "@/optimizer/optimizer.helper.class";
+
+let originalRandom: () => number;
+
+beforeAll(() => {
+  originalRandom = Math.random;
+});
+afterAll(() => {
+  Math.random = originalRandom;
+});
+
+describe("acceptWorseWithThres", () => {
+  it("should return true if new is smaller than old", () => {
+    expect(acceptWorseWithThres(10, 20, -1)).toBeTruthy();
+  });
+
+  it("should likely return true thres=auto and new approx old", () => {
+    Math.random = () => 0.1;
+    expect(acceptWorseWithThres(21, 20, -1)).toBeTruthy();
+  });
+  it("should likely return false thres=auto and new far off old", () => {
+    Math.random = () => 0.1;
+    expect(acceptWorseWithThres(200, 20, -1)).toBeFalsy();
+  });
+  it("should likely return true if le than thres, independent of how much worse new is", () => {
+    Math.random = () => 0.1;
+    expect(acceptWorseWithThres(21, 20, 0.1)).toBeTruthy();
+    expect(acceptWorseWithThres(22, 20, 0.1)).toBeTruthy();
+    expect(acceptWorseWithThres(2200, 20, 0.1)).toBeTruthy();
+  });
+  it("should likely return false if higher than thres, independent of how much worse new is", () => {
+    Math.random = () => 0.2;
+    expect(acceptWorseWithThres(21, 20, 0.1)).toBeFalsy();
+    expect(acceptWorseWithThres(22, 20, 0.1)).toBeFalsy();
+    expect(acceptWorseWithThres(2200, 20, 0.1)).toBeFalsy();
+  });
+  it("should not return true if thres is 0 and the new one is worse (default)", () => {
+    Math.random = () => 0.2;
+    expect(acceptWorseWithThres(21, 20, 0)).toBeFalsy();
+    expect(acceptWorseWithThres(22, 20, 0)).toBeFalsy();
+    expect(acceptWorseWithThres(2200, 20, 0)).toBeFalsy();
+    Math.random = () => 0.1;
+    expect(acceptWorseWithThres(21, 20, 0)).toBeFalsy();
+    expect(acceptWorseWithThres(22, 20, 0)).toBeFalsy();
+    expect(acceptWorseWithThres(2200, 20, 0)).toBeFalsy();
+    Math.random = () => 0.00001;
+    expect(acceptWorseWithThres(21, 20, 0)).toBeFalsy();
+    expect(acceptWorseWithThres(22, 20, 0)).toBeFalsy();
+    expect(acceptWorseWithThres(2200, 20, 0)).toBeFalsy();
+    Math.random = () => 0.9;
+    expect(acceptWorseWithThres(21, 20, 0)).toBeFalsy();
+    expect(acceptWorseWithThres(22, 20, 0)).toBeFalsy();
+    expect(acceptWorseWithThres(2200, 20, 0)).toBeFalsy();
+  });
+});
diff --git a/test/test-helpers.ts b/test/test-helpers.ts
index 735bc15..7ae5c86 100644
--- a/test/test-helpers.ts
+++ b/test/test-helpers.ts
@@ -55,6 +55,7 @@ export function getTestArgs(filename: string): OptimizerArgs {
     objectiveFunction: "cycles",
     uicaarch: "RKL",
     spilling: "reversebell",
+    threshold: 0,
   };
 }