How long should you train before entering a half marathon?

Firstly, the length of time to train for a half marathon will depend on your natural physical activity, your routine running, general health, age, sex, weight etc. Ideally your training schedule should be 10-12 weeks with varied intensity. However, before you enter this staggered intensity schedule, you should be comfortable running for 30 minutes. It can take a fortnight or more to get your body used to running depending on how active you are to start with. RunnersWorld have a wide variety of training plans, check them out for expert advice.