Starts with your running
With your permission, Build42 can use the recent runs stored in Apple Health on your phone. No useful history there? You can simply tell us how often and how far you have been running.
How Build42 works
A running plan built around you.
Build42 uses research-based training methods to create a tailored plan for your goal—one that works around your running history, the days you can train and the rest of your life.
Fits around your week
Choose the days you can train and the days that suit a Long run. Add holidays, unavailable dates or a lighter period, and your plan works around them.
Changes when life does
Miss a run, change your availability or need an easier spell? Build42 can reshape the training still ahead—without quietly replacing the plan you already accepted.
Your plan, step by step
Tell us where you want to go. Build42 works out a sensible route.
Choose a 5 km, 10 km, Half Marathon or Marathon goal. You can train for a particular event and date, or simply work towards the distance in your own time.
Build42 looks at what you have been running recently, how many days you can realistically train and any limits you have added. It then uses clear training rules to choose the run types, distances and recovery weeks that make up your plan.
If you add a target time, Build42 can show the pace needed to achieve it and use that as your Event-pace guide. If you do not add one, it will not invent a pace or pretend it can predict your finish time.
Made for real life
A good plan should bend before it breaks.
Training rarely goes exactly as expected. Build42 takes account of holidays, busy days, lighter weeks and the runs you actually complete. It will not cram missed distance into a catch-up session or fill every free day just because it can.
When a change affects future training, you see what will be different before deciding whether to update the plan.
A longer Marathon journey
More than 16 weeks to your Marathon? Start with Foundation.
Rather than stretching one Marathon schedule across many months, Build42 can begin with a Foundation plan based on the running you can manage now.
Foundation gradually prepares you for the focused 16-week Marathon plan. As the handover approaches, Build42 checks the running you actually completed and shows you the next plan before anything changes.
If the time or training available is not enough to reach the usual preparation level, Build42 says so plainly and offers practical choices. It does not hide the gap or promise an outcome.
For those who want to look under the bonnet
Plan details
Build42 keeps the main experience simple, but the rules behind the plan are not a secret. Open any section below to see the numbers, methods and limits in more detail.
What information does Build42 use?
With permission, Build42 reads running Workouts from Apple Health. If there is no useful Health history—or you prefer not to connect it—you can enter how often and how far you have run recently.
Your plan can also use your chosen distance, optional event name and date, optional target time, available running days, preferred Long-run days, holidays, lighter periods and current training-status answer.
The planning happens on your device. Missing information stays missing: Build42 does not invent running history, an event date or a target pace.
How long is each training plan?
The normal focused plan is 8 weeks for 5 km, 10 weeks for 10 km, 12 weeks for a Half Marathon and 16 weeks for a Marathon.
| Goal | Shortest plan offered when suitable | Normal focused plan | Longest focused plan considered |
|---|---|---|---|
| 5 km | 6 weeks | 8 weeks | 12 weeks |
| 10 km | 8 weeks | 10 weeks | 16 weeks |
| Half Marathon | 10 weeks | 12 weeks | 16 weeks |
| Marathon | 16 weeks | 16 weeks | 16 weeks |
For Version 1, the longer 5 km, 10 km and Half Marathon figures are supporting guidance rather than active cut-offs. A long-dated Marathon can use Foundation before its 16-week focused plan.
How quickly can the running increase?
Weekly distance normally increases by no more than 10%. A consistent recent running history can support a history-led limit of up to 15%.
Long runs are checked separately. The next Long run is normally limited to 10% above the longest qualifying completed—or still-planned—Long run in the previous 30 days. Recovery weeks normally reduce the load after three additional build weeks.
These are planning limits, not a claim that one percentage is safe or ideal for every runner. Build42 also respects holidays, unavailable days and 25% or 50% lighter periods.
What does “Limited preparation” mean?
Build42 compares the longest planned run with a preparation guide: 4.5 km for a 5 km goal, 8 km for 10 km, about 18 km for a Half Marathon and about 31.7 km for a Marathon.
If the plan cannot reach that guide in the time and training days available, it is labelled Limited preparation. You can still review the plan, but Build42 explains the shortfall and suggests practical alternatives such as allowing more time or more training days.
The label is not a medical decision, a readiness score or a prediction that you will—or will not—finish your event.
How does the 16-week Marathon plan work?
The focused Marathon plan has 3 Foundation weeks, 6 Development weeks, 4 Marathon-specific weeks and a 3-week Taper.
Easy and Aerobic running build the base. Long runs develop the ability to keep going. Controlled runs add sustained, purposeful work. Event-specific running introduces work at the pace and demands of the goal. The Taper reduces training before event day while retaining some running.
For a Marathon further away, the earlier Foundation stage builds towards the lowest weekly and Long-run starting point the focused plan needs for the runner’s chosen availability. Once that level is reached, Foundation maintains it rather than continuing to add distance.
What research and published plans informed Build42?
Plan-length choices were informed by published B.A.A. 5 km, 10 km, Half Marathon and Marathon plans, London Marathon’s 16-week plans, and New York Road Runners Marathon material.
The supporting research includes recreational Half Marathon and Marathon preparation, a recent review of tapering in endurance athletes, the earlier taper evidence, and the relationship between single-session distance changes and the preceding 30 days of running.
Published plans and research involving groups of runners cannot prove the perfect plan for one person. Build42 uses them to set transparent boundaries; it does not diagnose injury, provide medical clearance, guarantee a result or claim that its plan is universally optimal.
Clear enough to follow. Flexible enough for real life.
That is what Build42 is designed to deliver: a plan with a reason behind it, shaped around the runner who has to live it.