How to increase your running mileage safely

The 10% rule says you should not raise your weekly distance by more than 10% from one week to the next. It is easy to remember and it pushes people to build slowly. That is its value.

The research is less tidy. A Dutch randomized trial gave 532 novice runners either a standard 8-week plan or a gentler 13-week plan based on the 10% rule. Injury rates were almost identical: 20.8% in the graded group and 20.3% in the standard group. A Danish study of 874 new runners found no overall difference between those who increased weekly distance by under 10%, 10–30%, or more. It did hint that jumps over 30% in two weeks were linked with more distance-related injuries such as runner’s knee and shin pain.

A 2025 study tracked 5,205 adult runners through their GPS watches for 18 months. Weekly changes in distance were not clearly linked to injury. Single runs were. When one run was more than 10% longer than the longest run in the previous 30 days, the rate of overuse injury went up. The bigger the spike, the higher the rate.

This is observational research, so it shows a link rather than proof. It still points to a practical rule: grow your long run in small steps, and do not suddenly double a run because you feel good.

This takes a runner from about 10 to about 15 miles a week over eight weeks, with the longest run growing in steps of about 10%.

Keep the extra miles easy. Do not add speed work in the same weeks you add a lot of distance.

Ranges vary a lot from plan to plan. These are typical for first-timers running three or four days a week:

If you are well below the starting number for your goal, give yourself extra weeks rather than steeper steps. The plans in the 10K guide and half marathon guide follow these ranges.

• Very low mileage. At 5 miles a week, 10% is half a mile. You can add a whole extra short run, as long as the longest run stays the same.
• After a break. Coming back from a few weeks off, start below your old level and build back over several weeks.
• Already high mileage. At 30 or 40 miles a week, 10% is a big absolute jump. Smaller steps are often wiser.
• After an injury. Return slowly, and follow your doctor or physical therapist’s plan rather than any rule of thumb.

Adding a day often goes down better than making every run longer. Three runs of 3 miles feel different from two runs of 4.5.

The American Academy of Orthopaedic Surgeons describes stress fractures as overuse injuries that often follow a rapid increase in activity. Pain usually starts in one spot on a bone, shows up during or after exercise, and eases with rest. As it worsens it can hurt during everyday walking.

• Pain in one spot that gets worse as you run.
• Pain that makes you limp or change your stride.
• Swelling, or aching at night.
• Pain that is still there after a few days of rest.

Any of these means stop running and see a doctor. Read about shin splints and knee pain from running for the common ones.

• Sleep and rest days. At least one full rest day a week. See rest days and sleep for runners.
• Enough food. Running more on fewer calories raises the risk of bone stress injuries.
• Shoes that are not worn out, and softer surfaces when you can.
• Strength work twice a week. The strength training guide has a routine.
• Cross-training. Cycling, swimming or walking build fitness with less impact.

You cannot build gradually without knowing where you are. Write down, or let an app record, three numbers each week:

1. Total distance for the week.
2. Your longest single run, and your longest in the past four weeks.
3. How your body feels, on a simple 1–5 scale.

Before each long run, check the second number. If today’s plan is more than about 10% longer than your longest recent run, trim it. The track your running progress guide covers what else is worth logging.

• Making up a missed week by doubling the next one.
• Following 10% for weekly totals but adding all of it to the long run.
• Building distance and speed in the same weeks.
• Never taking a down week because you feel fine.
• Treating a new pain as soreness for a week before resting.

Longer challenges reward steady weeks over big ones. DRAGON is 179 km in 88 days, about 2 km (1.3 miles) a day. Walks count too, so you can keep easy days easy. Shorter goals like ODIN or THOR fit inside a normal training week. The X Challenge app adds up every session, which makes it easy to see your weekly total at a glance.

• Is the 10% rule a myth? Not a myth, but not proven either. Use it as a rough ceiling, and watch your longest run.
• How many miles a week for a half marathon? Many first-timers peak somewhere around 15 to 25 miles a week.
• Should I take a down week? Yes. An easier week every three or four weeks lets your body catch up.
• Does walking count toward mileage? It counts toward fitness and toward an X Challenge total, with less impact than running.

If you have a health condition, are pregnant, or have not exercised in a long time, check with a doctor before you start.

• Buist I. et al. No effect of a graded training program on the number of running-related injuries in novice runners. Am J Sports Med, 2008
• Nielsen R.O. et al. Excessive progression in weekly running distance and risk of running-related injuries. J Orthop Sports Phys Ther, 2014
• Frandsen J.S.B. et al. How much running is too much? Identifying high-risk running sessions in a 5200-person cohort study. Br J Sports Med, 2025
• Stress Fractures, OrthoInfo (American Academy of Orthopaedic Surgeons)