What Is the 10 Percent Rule?

Dear Fit,
I signed up for a marathon in the Fall, but since I'm used to running only about three miles now, it means I'm going to have to start increasing the distance for my runs. A runner friend mentioned that I need to follow the 10 percent rule to prevent overexerting or injuring myself. I read about it, but it's a little confusing, and I'm not sure how to implement it into my training. Can you explain what this would look like as far as mileage goes?
—Perplexed by the 10 Percent Rule

This is a great question, especially considering that many people's enthusiasm for running has probably increased just as the temps have. Plus, the wide trails and fresh warm air make you feel like you can run forever. So before you go from 10 miles last week to 30 miles this week, you must obey the 10 percent rule. It's a way to gradually increase your mileage while preventing overuse injury and allowing your body time to adapt.

To see what this rule means when it comes to how many miles you run, check out the chart I made after you read more.

The 10 percent rule states: never increase your weekly mileage by more than 10 percent as compared to the previous week. Let's say you're starting off with running 10 miles (two miles each day). Check out the chart below to see how many miles you should increase each week. Most people run about 12 to 20 miles a week, so you can stop increasing once you reach your weekly mileage amount.