Marathon Training Plan: 12, 16, 18, 20 or 24 Weeks
A marathon plan in five lengths, 12 to 24 weeks. Sixteen is the favourite: time to build base and marathon fitness, and start fresh.
The plan, week by week
Minutes per week. Tap a week.Pick your plan length
The chart above is the one marked “shown”. Ask Claude for any of these and it builds that one, paced from your own runs.
| Version | Weeks | Weeks of each phase |
|---|---|---|
| 12 weeks | 12 | 4 base · 4 build · 1 peak · 3 taper |
| 16 weeks (shown) | 16 | 5 base · 5 build · 3 peak · 3 taper |
| 18 weeks | 18 | 6 base · 6 build · 3 peak · 3 taper |
| 20 weeks | 20 | 7 base · 7 build · 3 peak · 3 taper |
| 24 weeks | 24 | 8 base · 8 build · 5 peak · 3 taper |
A 16-week marathon training plan designed for runners with a clear goal and a defined timeline. The marathon is fundamentally an aerobic event with a metabolic ceiling problem. Running out of glycogen — 'the wall' — is a fuelling and pacing failure, not a fitness failure. The training goal is to build a large enough aerobic base, develop fat oxidation efficiency, and practice race-pace running so the body knows what's coming on race day.
Choosing a marathon block length
The right marathon block depends on your base. Runners who already run 40 km or more a week, with long runs of 90 minutes, can build to a marathon in a shorter block. If you are coming from lower mileage, the longer blocks give the long run time to grow to 30 km or so without big jumps, and leave room for the illness, travel and life that will interrupt a four-to-six-month build. A shorter block on too little base is the most common route to a sore, slow last 10 km.
The phases of a medium-length training block
A 16-week plan splits into 4 phases: 5 weeks of base, 5 of build, 3 at peak and a 3-week taper. Understanding which phase you're in helps you interpret what the sessions are trying to accomplish.
Building progressive overload safely
Medium-length training blocks allow for proper periodisation: load builds over three weeks, drops on the fourth recovery week, then builds again from a higher baseline. Never skip recovery weeks — they're when adaptation happens. The recovery week feels like a step backward but delivers a step forward.
Race-week management
The final week before race day is about feeling fresh, not building fitness — that work is done. Keep sessions short, maintain intensity with one or two race-pace efforts of 60–90 seconds, stay off your feet more than usual, and sleep aggressively. The taper itch (restlessness, phantom soreness, doubt) is normal and almost always resolves on race morning.
Why more weeks mean more base
An 18-week plan gives you something shorter plans cannot: a genuine aerobic base-building phase before the race-specific work begins. The extra weeks in the first phase aren't just adding mileage — they're building mitochondrial density, bone resilience, tendon strength, and fat oxidation capacity that the specific fitness phase and taper then convert into race-day performance.
Managing the mental length of a long build
Training for 20+ weeks is a long time to stay motivated and injury-free. Race simulations, parkruns, and tune-up races every four to six weeks provide short-term goals and honest fitness feedback. They also break the long block into sub-blocks that feel more manageable. With Daash, Claude checks each week's training against the plan, so you stay aligned.
Knowing when to modify the plan
A long plan has many more opportunities for illness, life events, and fatigue to interfere. The rule is to modify rather than abandon: reduce volume rather than stopping, convert a quality session to easy running rather than resting, and always protect the long run. A modified week followed by a normal week does less damage than complete rest followed by trying to catch up.
Questions
How many days per week does this marathon plan require?
Most sessions in this plan run four to five days per week, including one quality session, a long run, and easy aerobic running. The plan is designed to be adjustable — with Daash, Claude can restructure it around your available days each week.
Do I need a GPS watch to follow this marathon training plan?
A GPS watch or running app is helpful for tracking pace and distance, but not strictly required. Effort-based running (using a scale of 1–10 perceived exertion) works well for easy runs. For quality sessions where specific paces matter, a watch becomes more valuable.
What should I eat before a long run?
For runs under 60–75 minutes, eating beforehand is optional. For longer runs, a light carbohydrate-based meal two to three hours before the session — oats, toast with banana, or a rice-based option — provides fuel without gastrointestinal issues. Avoid high-fat, high-fibre, or unfamiliar foods on long run mornings.
How does Daash adapt the plan if I miss a session?
Daash sees missed sessions in your Garmin data. Tell Claude why — illness, fatigue, life — and it reworks the coming week: redistributing sessions, reducing volume if needed, or adjusting the next quality session, then updates the workouts on your watch.
Do I need to take gels or nutrition during training for a marathon?
For any long run over 90 minutes, practising race nutrition is valuable. Train with the gels, chews, or drinks available at your target race so your gut is adapted before race day. Do not try a new nutrition product for the first time on race morning.