>Running 101>How to train for a half marathon (Can only run 2.5 miles max)
You are doing just fine without a heart rate monitor. If you really want to monitor your heart rate, you will want to know your maximum heart rate. A 5K race is a good way to estimate your maximum heart rate.
You are ready to run a 5K race. If you push yourself hard enough in a 5K, you should see at about 98% of your maximum heart rate toward the end. Your 5K race time, with or without heart rate, is good for calculating appropriate training run speeds.
I strongly recommend that you check this out half marathon running programs. They offer a bunch of free running programs at all types of fitness levels. Hope this helps and good luck on your training!