Short answer: Yes, you run two marathons in the same season, or at least in the same year.
However, we’d humbly suggest that you already have at least one to your name before you consider piling them onto your calendar. It will be helpful to know how your body responds to training, and how quickly it recovers from a long race.
When you feel ready to take on this challenge, we’d suggest attempting your two marathons in alternate seasons of the same year. In other words, instead of trying to compete both marathons back-to-back, schedule one marathon for spring and another for fall, which will give you roughly 6 months to recover and then build up for the second race.
A typical marathon training schedule consists of four 10–12-week cycles, with a week or so of recovery between. These cycles are
This adds up to a full year of preparation. No problem for that first marathon, but how do you cope with marathon number two, which comes just six months later? It’s not really a problem, because you’re not starting from scratch.
You’ll need to recover after that big race. Be patient here, or you’ll risk injury or overtraining. You may choose to take a full week off of running, and then run easily for two weeks, revisiting the kind of easy run you did during the foundation-building phase. Then you’ll want to do a full cycle of 10K training, to get your speed back, and finally a full cycle of marathon training to get your endurance back. It will look something like this:
You could also give yourself more time, by, say, running your first marathon in the winter and your second one in the fall. This would allow you to spread your recovery and training over 9 months instead of 6.
However, splitting the calendar evenly with a spring / fall calendar will allow you to continue running two marathons every year. With a 9-month split, you’re really running 1-1/2 marathons a year—so on alternating years you’ll only be able to run one.
The spring / fall calendar also offers the greatest choice of races, and in most climates, the most favorable weather.
In summary, our advice is to go for it, as long as you have enough experience to know you’re up for the challenge. Just be sure to listen to your body, especially when it comes to recovering from that first big race. Better to take it a bit easy than to sideline yourself with an injury.