diff --git a/llvm/utils/lit/lit/ProgressBar.py b/llvm/utils/lit/lit/ProgressBar.py
--- a/llvm/utils/lit/lit/ProgressBar.py
+++ b/llvm/utils/lit/lit/ProgressBar.py
@@ -253,7 +253,7 @@
             elapsed = time.time() - self.startTime
             if percent > .0001 and elapsed > 1:
                 total = elapsed / percent
-                eta = int(total - elapsed)
+                eta = total - elapsed
                 h = eta//3600.
                 m = (eta//60) % 60
                 s = eta % 60
diff --git a/llvm/utils/lit/lit/display.py b/llvm/utils/lit/lit/display.py
--- a/llvm/utils/lit/lit/display.py
+++ b/llvm/utils/lit/lit/display.py
@@ -5,8 +5,10 @@
     if opts.quiet:
         return NopDisplay()
 
-    of_total = (' of %d' % total_tests) if (tests != total_tests) else ''
-    header = '-- Testing: %d%s tests, %d workers --' % (tests, of_total, workers)
+    num_tests = len(tests)
+    of_total = (' of %d' % total_tests) if (num_tests != total_tests) else ''
+    header = '-- Testing: %d%s tests, %d workers --' % (
+        num_tests, of_total, workers)
 
     progress_bar = None
     if opts.succinct and opts.useProgressBar:
@@ -21,6 +23,42 @@
     return Display(opts, tests, header, progress_bar)
 
 
+class ProgressPredictor(object):
+    def __init__(self, tests):
+        self.completed = 0
+        self.time_elapsed = 0.0
+        self.predictable_tests_remaining = 0
+        self.predictable_time_remaining = 0.0
+        self.unpredictable_tests_remaining = 0
+
+        for test in tests:
+            if test.previous_elapsed:
+                self.predictable_tests_remaining += 1
+                self.predictable_time_remaining += test.previous_elapsed
+            else:
+                self.unpredictable_tests_remaining += 1
+
+    def update(self, test):
+        self.completed += 1
+        self.time_elapsed += test.result.elapsed
+
+        if test.previous_elapsed:
+            self.predictable_tests_remaining -= 1
+            self.predictable_time_remaining -= test.previous_elapsed
+        else:
+            self.unpredictable_tests_remaining -= 1
+
+        # NOTE: median would be more precise, but might be too slow.
+        average_test_time = (self.time_elapsed + self.predictable_time_remaining) / \
+            (self.completed + self.predictable_tests_remaining)
+        unpredictable_time_remaining = average_test_time * \
+            self.unpredictable_tests_remaining
+        total_time_remaining = self.predictable_time_remaining + unpredictable_time_remaining
+        total_time = self.time_elapsed + total_time_remaining
+
+        return self.time_elapsed / total_time
+
+
 class NopDisplay(object):
     def print_header(self): pass
     def update(self, test): pass
@@ -30,8 +68,10 @@
 class Display(object):
     def __init__(self, opts, tests, header, progress_bar):
         self.opts = opts
-        self.tests = tests
+        self.num_tests = len(tests)
         self.header = header
+        self.progress_predictor = ProgressPredictor(
+            tests) if progress_bar else None
         self.progress_bar = progress_bar
         self.completed = 0
 
@@ -55,7 +95,7 @@
         if self.progress_bar:
             if test.isFailure():
                 self.progress_bar.barColor = 'RED'
-            percent = float(self.completed) / self.tests
+            percent = self.progress_predictor.update(test)
             self.progress_bar.update(percent, test.getFullName())
 
     def clear(self, interrupted):
@@ -66,7 +106,7 @@
         # Show the test result line.
         test_name = test.getFullName()
         print('%s: %s (%d of %d)' % (test.result.code.name, test_name,
-                                     self.completed, self.tests))
+                                     self.completed, self.num_tests))
 
         # Show the test failure output, if requested.
         if (test.isFailure() and self.opts.showOutput) or \
diff --git a/llvm/utils/lit/lit/main.py b/llvm/utils/lit/lit/main.py
--- a/llvm/utils/lit/lit/main.py
+++ b/llvm/utils/lit/lit/main.py
@@ -205,8 +205,7 @@
 
 def run_tests(tests, lit_config, opts, discovered_tests):
     workers = min(len(tests), opts.workers)
-    display = lit.display.create_display(opts, len(tests), discovered_tests,
-                                         workers)
+    display = lit.display.create_display(opts, tests, discovered_tests, workers)
 
     run = lit.run.Run(tests, lit_config, workers, display.update,
                       opts.max_failures, opts.timeout)