Analysis · Plan basics
How many weeks do you need, by starting mileage?
Our planner's answers for the 5K, 10K and half marathon across six starting mileages, under stated assumptions including run-time limits.
“How long should I train for a half marathon?” has no single answer, because it depends on where you start and how much time you can give each run. Instead of one number, we asked our own planner.
How we generated the table
For each goal (5K, 10K and half marathon) and each starting mileage from 5 to 30 miles a week, we ran the planning engine for every race timeline from 4 to 30 weeks. We recorded two things:
- Any plan: the fewest weeks for which the planner writes a plan at all.
- Reaches targets: the fewest weeks for which the plan reaches the weekly mileage and long run it aims for at that experience level.
The planner is deterministic, so the same inputs always give the same answers. The tables below are generated each time the site is built, so they match the planner’s current rules.
The assumptions matter, and one of them matters a lot: how long a run is allowed to last. The first table caps regular runs at 60 minutes and the long run at 2 hours. The second allows 90 minutes and 2.5 hours. Because weekly mileage is limited by how far each run can go in the time allowed, the same runner can need many more weeks, or never reach the plan’s targets, under the shorter limit. Both limits are choices we made, not facts about runners.
How to read it
A shorter timeline than the “Any plan” column is one the planner will decline, because a gradual build cannot get from your current running to the goal in that time. A timeline between the two columns gets a plan, but one that ends below its usual targets. Longer than the “Reaches targets” column, the plan reaches the mileage and long run the planner aims for.
Two patterns are worth noticing:
- Lower starting mileage needs more weeks. Mileage rises in small steps and the long run grows by at most a mile a week, so a larger gap takes longer to close.
- Longer races ask more. The half marathon needs a higher peak week and a longer long run than the 5K, so it needs more runway from the same starting point.
What this does not tell you
- It trusts the numbers you give it. The planner cannot check your mileage, health or injury history, and a recent injury means it will not generate a plan at all.
- It is not a prediction. “Reaches targets” means the plan gets to the planner’s own mileage targets, not that you will finish or run any particular time.
- It is not medical advice. Talk to a doctor before starting a new training program, especially with a health condition or pain.
- The experience levels and run-time limits are assumptions. We paired each starting mileage with an experience level and runs per week, and capped run times, as listed under each table. Your own answers may differ and change the result.
Use your own numbers
The table is a set of examples. The race readiness checker runs the same planner on your own goal, timeline and weekly miles, and tells you whether a gradual build fits.
What this article is based on
Engine statements. Statements about what the planner does come from its published rules and outputs. See How It Works and Our method.
Written by the Milewell team and published on the site owner's approval. The owner is not a credentialed coach or clinician, and this article has not been reviewed by one. See our editorial policy.
This plan is general training information, not medical advice and not clearance to exercise. Stop and get professional advice if you feel pain, dizziness, chest discomfort or unusual shortness of breath. If you have a health condition or are unsure whether running is right for you, talk to a doctor first.