How Many Weeks to Train for a Half Marathon?

Most runners need 12 weeks to train for a half marathon, but the right number is 8 if you already run 15 or more miles a week and 16 if your running base is closer to a 5k. The count depends on what you can do now, not on the race. For the Indy Mini on Saturday, May 8, 2027, that puts your start line on March 13, February 13 or January 16. If you want a coach to check which path is yours, the free consultation covers it, and the first half marathon after 40 guide explains the build itself.

Pick your path by what you run this week

Count your running over the last four weeks, including run-walk intervals, then use this table.

What you do now	Your path	Start for May 8, 2027
About 15 or more miles a week, long run near 6	8 weeks	Saturday, March 13
About 8 to 15 miles a week, long run 3 to 5	12 weeks	Saturday, February 13
Under 8 miles a week, or just finished a first 5k	16 weeks	Saturday, January 16
Not running yet	Add 4 to 6 weeks of walk-jog before week 1	Early December

If you sit between two rows, take the longer one. A half marathon has a long tail of fatigue in the last three miles, and the extra weeks are what you spend on it.

What the 8 week path really is

Eight weeks is a sharpening block, not a beginner build. The long run climbs by a mile or so a week to about 10 or 11 miles, one week in the middle drops back, and the last week is a taper. It works when your tendons and calves have already adapted to regular running. It fails when a person with a 5k base reads “8 weeks” and starts at week one with a long run twice as far as anything they have done.

Why 12 weeks is the default

Twelve weeks allows two build weeks, a down week, two more build weeks and so on, with the final three weeks for the peak and the taper. It lets you add roughly a mile to the long run most weeks without crossing the rule of thumb that total weekly mileage should not jump by more than about 10 percent. It also leaves a spare week or two for a cold, a work trip or a bad night. Most first-timers who finish comfortably are on this path.

When 16 weeks is the better answer

Choose 16 if any of these describe you:

• You are returning after a long break, an injury or a baby.
• You are over 40 and your last run was a while ago.
• You are carrying extra body weight and want gentler loading on joints.
• You want two lifting days a week alongside three runs without adding fatigue.

On this path the first four weeks are run-walk work. Those weeks are not wasted. They are the reason the build in weeks 9 to 14 feels manageable. The Indy Mini strength guide shows how to place the lifting around the long run.

What to do with the weeks you do not use

If you have more time than your path needs, do not stretch the plan thinner. Spend the surplus on a 5k or 10k tune-up, or on a strength block that you finish before the build begins. Lifting two days a week for a month before running volume rises is one of the lowest-risk ways to make the later weeks easier. A coach can place that block, and FlexWerk’s private suites near the Monon Trail in Carmel City Center rent by the hour, so you can fit it around work without a membership. Each coach sets their own format and rate.

A quick decision checklist

1. Write down your weekly miles and longest run from the last four weeks.
2. Match them to the table and pick the longer path if torn.
3. Count back from race day to find your start date, and put a down week on every fourth week.
4. Add one buffer week if you travel, have kids’ schedules or work a seasonal peak in the build.
5. Book your first two long runs and your lifting days on the calendar before you start.

Once the start date is on the calendar, the next step is making the first week small enough to repeat.