diff --git a/app/config.py b/app/config.py
index f2d5b44..436faeb 100644
--- a/app/config.py
+++ b/app/config.py
@@ -1,3 +1,4 @@
 # 16 quadrillion
 MAX_NUM = 16_000_000_000_000_000
 DEFAULT_COUNTING_SPEED = 57_000 // 2
+MAX_RUNNING_TIME_SECONDS = 5 * 60
diff --git a/app/math_game.py b/app/math_game.py
index 6d0b11d..3433099 100644
--- a/app/math_game.py
+++ b/app/math_game.py
@@ -1,7 +1,7 @@
 # (c) 2020 Simon Averbach and Zev Averbach
 from time import sleep
 
-from config import MAX_NUM, DEFAULT_COUNTING_SPEED
+from config import MAX_NUM, DEFAULT_COUNTING_SPEED, MAX_RUNNING_TIME_SECONDS
 
 
 def math_game():
@@ -24,6 +24,20 @@ def math_game():
     else:
         num_counts_per_second = int(num_counts_per_second_string)
 
+    predicted_running_time_seconds = int((number / each) / num_counts_per_second)
+    while predicted_running_time_seconds > MAX_RUNNING_TIME_SECONDS:
+        print(f"Sorry, that would run for {predicted_running_time_seconds:,} seconds, which is greater than "
+              f"the maximum allowed of {MAX_RUNNING_TIME_SECONDS:,} seconds.")
+        suggested_num_counts_per_second = int((number / each) / MAX_RUNNING_TIME_SECONDS)
+        print(f"I suggest you run a minimum of {suggested_num_counts_per_second:,} counts per second.")
+        print(f"How many counts do you want to do per second? [{suggested_num_counts_per_second:,}]")
+        num_counts_per_second_string = input("> ")
+        if num_counts_per_second_string == '':
+            num_counts_per_second = suggested_num_counts_per_second
+        else:
+            num_counts_per_second = int(num_counts_per_second_string)
+        predicted_running_time_seconds = (number / each) / num_counts_per_second
+
     print(f"Okay, here we go! We're going to count from zero to {number}, "
           f"adding {each} {num_counts_per_second} times per second.")
     sleep(3)