diff --git a/src/Slicer.js b/src/Slicer.js
index a0a7069..e8f4f5b 100644
--- a/src/Slicer.js
+++ b/src/Slicer.js
@@ -47,6 +47,11 @@ export default class {
             resolve(data.gcode);
             break;
           }
+          case 'PROGRESS': {
+            if (this.onprogress) {
+              this.onprogress(data);
+            }
+          }
         }
       });
 
diff --git a/src/sliceActions/slice.js b/src/sliceActions/slice.js
index 2b3f47f..7ddcb65 100644
--- a/src/sliceActions/slice.js
+++ b/src/sliceActions/slice.js
@@ -13,32 +13,53 @@ import applyPrecision from './applyPrecision.js';
 import removePrecision from './removePrecision.js';
 
 export default function(geometry, settings) {
-  geometry.mergeVertices();
-  geometry.computeFaceNormals();
+  const totalStages = 15;
+  let current = 0;
+  const progressMessage = () => {
+    current++;
+    postMessage({ message: 'PROGRESS', data: { done: current, total: totalStages } });
+  };
 
+  geometry.mergeVertices();
+  progressMessage();
+  geometry.computeFaceNormals();
+  progressMessage();
   // get unique lines from geometry;
   const openClosed = detectOpenClosed(geometry);
+  progressMessage();
   const lines = createLines(geometry, settings, openClosed);
+  progressMessage();
 
   const {
     layerIntersectionIndexes,
     layerIntersectionPoints
   } = calculateLayersIntersections(lines, settings);
+  progressMessage();
 
   const shapes = intersectionsToShapes(layerIntersectionIndexes, layerIntersectionPoints, lines, settings);
+  progressMessage();
 
   applyPrecision(shapes);
+  progressMessage();
 
   const slices = shapesToSlices(shapes, settings);
+  progressMessage();
 
   generateInnerLines(slices, settings);
+  progressMessage();
   generateInfills(slices, settings);
+  progressMessage();
   generateSupport(slices, settings);
+  progressMessage();
   addBrim(slices, settings);
+  progressMessage();
   optimizePaths(slices, settings);
+  progressMessage();
   removePrecision(slices);
+  progressMessage();
 
   const gcode = slicesToGCode(slices, settings);
+  progressMessage();
 
   return gcode;
 }