How long should a half marathon training plan be?
Twelve weeks is the standard baseline, and it exists for a reason. Below ten weeks, you don't have enough time to build aerobic capacity safely and still taper. Beyond sixteen weeks, most amateur runners plateau or burn out before race day.
If you have more than twelve weeks available, don't start your plan immediately. Use the extra weeks to build a comfortable easy-run base — three runs a week at conversational pace. Starting the formal plan with more aerobic base behind you means your body responds faster to the quality sessions.
If you have fewer than ten weeks, the plan still works, but prioritise completing the long runs over the speed sessions. Finishing is always better than skipping weeks to cram in quality.
How many days a week should you run?
Three to five days a week covers the full range for amateur runners. Four days is the most common sweet spot — it gives you enough volume to adapt without the injury risk that comes with running every day.
Three days works if you're consistent with it. The key is making sure those three runs include a long run, one quality session (tempo or intervals), and one easy recovery run. Skipping any of the three types in favour of doing three easy runs won't improve your fitness enough to hit a time goal.
Five days is appropriate if you've been running consistently for at least a year and have no history of overuse injury. Adding a fifth day provides more aerobic stimulus, but the gains diminish quickly — many runners see the same results from four structured days versus five unstructured ones.
- →3 days/week: long run + one quality session + one easy run
- →4 days/week: long run + tempo + speed or hills + easy run
- →5 days/week: long run + tempo + speed + two easy runs
The four phases of half marathon training
A well-structured plan doesn't just add mileage every week. It moves through four distinct phases, each with a different physiological target.
Base phase (weeks 1–3) builds your aerobic engine. Most runs are easy — conversational pace, low heart rate. The goal is to create the foundation that the later, harder work sits on. Skipping this phase is the most common mistake ambitious runners make.
Strength phase (weeks 4–6) introduces longer tempo runs and moderate hills. This is where your lactate threshold rises — the point at which running gets hard. Raising that threshold means you can hold a faster pace for longer before you start to struggle.
Speed phase (weeks 7–9) adds interval training and race-pace work. These sessions are the hardest of the plan. By this point your aerobic base is solid enough to handle them, and there's still enough time for your body to absorb the adaptation before you taper.
Taper phase (weeks 10–12) cuts volume by 30–50% while keeping intensity. You're not losing fitness — you're arriving at race day with fresh legs and a body that has fully absorbed the training load from the weeks before.
The 10% rule: how to build mileage safely
The 10% rule states that your total weekly mileage should increase by no more than 10% from one week to the next. It's the most evidence-backed guideline in recreational running for avoiding overuse injuries.
The rule matters most in the base and strength phases when volume is climbing. In the speed phase, volume often plateaus while intensity rises — the 10% cap still applies, but you're less likely to hit it.
Every third or fourth week should be a recovery week where total volume drops by 20–30%. This isn't a setback. It's when your body consolidates the adaptations from the previous three weeks. Runners who skip recovery weeks often find their speed sessions feeling harder rather than easier as the plan progresses.
What does a typical training week look like?
The distribution of effort across the week matters as much as the total volume. A common mistake is making every run moderately hard — this leaves you too tired for quality sessions but not easy enough to recover properly.
The 80/20 principle applies well here: roughly 80% of your weekly mileage at easy pace (conversational, low effort), 20% at quality pace (tempo, intervals, or race pace). This ratio applies whether you're running three days or five.
For a four-day week in the strength phase, a sensible structure might look like: Monday easy, Wednesday tempo (4–6 km at a comfortably hard pace), Friday rest, Saturday long run, Sunday easy or rest. The long run and the tempo are the week's two anchors — everything else exists to support them.
How to taper correctly for race day
Tapering is the part most runners get wrong. They either cut too much (arriving at the start line feeling sluggish) or not enough (arriving tired). The target is a 30–40% reduction in total volume over the final two to three weeks, with intensity maintained.
In the final week before your race, avoid anything faster than race pace. Two or three short easy runs are enough to keep your legs loose. You cannot gain meaningful fitness in the last seven days — you can only lose it by overtraining or protect it by resting.
The sluggish feeling many runners experience in the first week of taper — sometimes called 'taper madness' — is normal. Your legs feel heavy because your glycogen stores are filling back up, not because you're losing fitness.