The useful answer is a range, not one magic number
Count back from race day, but start the decision with what you have done lately: how many days you run in a normal week, how long your longest comfortable run has been, and whether you are returning after a break. A race distance by itself cannot tell you how quickly to prepare.
Choose a plan whose first week resembles your current routine. Add time to establish that starting point if it does not. More calendar space also makes room for rest, travel, illness, and weeks that do not go to plan; squeezing the same workload into fewer weeks does not create the same adaptation.
Sources for this section: U.S. Physical Activity Guidelines: increase gradually from your current level
What published plans actually assume
These are examples of program length, not promises that everyone will be race-ready on that schedule. Read the first week and the stated entry requirements before using the last week as your target.
- 5K: the NHS Couch to 5K program uses nine weeks of walk-run sessions, three days a week, with rest days between. That is one beginner path toward 30 minutes of running—not a universal minimum or a race-time guarantee.
- 10K: the Boston Athletic Association's Level One plan has a two-week preparation phase and nine-week main phase. Its first week already includes several 20- to 25-minute runs, so someone starting from no running needs a separate build-up first.
- Half marathon: a New York Road Runners conservative plan lasts ten weeks but explicitly starts from three to four running days a week and a longest run of about 40 minutes. The ten weeks do not include building that base from zero.
Sources for this section: NHS Couch to 5K plan · B.A.A. Level One 10K plan · NYRR conservative half-marathon plan
Work the calendar backward
- Write down the race date and count the actual weeks available, not just the month names.
- Find a plan for your goal and compare its first week with your last few ordinary weeks. If the jump is large, budget a separate base-building period or choose a later race.
- Mark travel, work peaks, and family commitments. Protect recovery days and an easier lead-in to the race rather than treating every date as a day to make up mileage.
- Recheck the plan after illness, persistent pain, or several missed weeks. Resume from the capacity you have, not the workout you were scheduled to complete on paper.
Two runners, one half-marathon date
Runner A has been running three or four days each week, with a comfortable 40-minute longest run. With ten uninterrupted weeks until a half marathon, a conservative plan with those entry requirements is a plausible comparison. They still need to check whether its weekly sessions fit work, recovery, and the course.
Runner B has the same race date but has not run regularly for months. The same ten-week plan starts above their current base. A shorter race, a later half marathon, or a low-pressure return to running is more honest than trying to catch up by stacking workouts.
When to change the goal
If the first week already feels like a stretch, the calendar has no room for ordinary interruptions, or pain changes how you run, reconsider the date or distance. A training plan is a tool for organizing work, not permission to override symptoms.
A qualified coach can help match a plan to experience and time. Seek appropriate medical advice when health conditions, injury, or persistent symptoms make generalized training guidance a poor fit.