There are two distinct types of runners who ask this question: the first-time half marathon runner who runs just 2 to 3 days a week for 3 to 5 miles.
On the other end of the spectrum is the runner who has raced several half marathons and wants to race faster. Thus, the key distinction between these two runners is the 13.1-mile distance—the first athlete has not run a 13.1-mile run whereas the second one has run 13.1 miles or longer several times.
When it comes to training for the half marathon, the key workout each week is the long run. If you make the long run the focus of your training, you give yourself a great shot of running well come race day. I like to see the first-time half-marathon runner give himself at least 12 weeks to train adequately for the race.
Assuming you’re doing 4 to 5 miles once a week, 12 weeks gives you plenty of time to build up to a 10- or 11-mile long run. You don’t necessarily need to run 13.1 miles in training to be confident that you can finish the 13.1-mile race, yet you don’t want your longest run to be just 8 miles. Getting up to the 10- to 11-mile distance for your weekly long run is the goal.
After that, you want to do one aerobic workout a week. Fartlek workouts, threshold workouts, longer aerobic repeats on a track or on a dirt path are all good options.
Once you’ve done that, you can get away with running just two more days a week to be prepared to run the race, giving you a total of four running days per week to be able to finish a half marathon. You should cross-train two days a week and then take one day a week off.
The schedule might look like this:
Monday: easy run
Tuesday: workout
Wednesday: cross-training
Thursday: cross-training
Friday: easy run
Saturday: long run
Sunday: off or brisk walk