You’ve got four days, not six. That’s enough. Four runs a week, built over 12 weeks, can carry most adults across a half marathon finish line healthy.
Most popular free plans assume 5 or more run days. If your week doesn’t allow that, you’ve probably felt behind before you started. You’re not.
A half marathon training plan on 4 days: the shape of the week
Keep four runs. Each has one job.
- Run A: easy. Short and relaxed.
- Run B: quality. Strides early, a tempo run or intervals later.
- Run C: easy. Same idea as Run A.
- Run D: the long run. This one is protected.
An easy run is a pace where you can talk in full sentences. A tempo run is comfortably hard, a pace you could hold for about 20 to 30 minutes. A long run is your longest run of the week, done slowly.
If life takes a day, drop Run A or C first. Keep the long run and the quality run. Easy miles are the cheapest to lose.
Here’s the 12-week build. Treat these numbers as coaching conventions, not study results. They’re a sensible starting point, and you should scale them to your own base. Weekly miles in the chart and table exclude the race itself.
Two dips, then a fall. That’s the whole shape.
The 12-week plan table
| Week | Phase | Miles (excl. race) | Long run | Run B (quality) | If you miss it |
|---|---|---|---|---|---|
| 1 | Base | 14 | 5 | 4 x 20 sec strides | Skip Run A |
| 2 | Base | 16 | 6 | 6 x 20 sec strides | Skip Run A |
| 3 | Base | 18 | 7 | 15 min tempo | Skip Run C |
| 4 | Down week | 14 | 5 | Easy with strides | Skip anything |
| 5 | Build | 20 | 8 | 20 min tempo | Skip Run C |
| 6 | Build | 22 | 9 | 5 x 3 min hard | Skip Run A |
| 7 | Build | 24 | 10 | 25 min tempo | Skip Run C |
| 8 | Down week | 19 | 7 | Easy with strides | Skip anything |
| 9 | Peak | 27 | 11 | 25 min tempo | Skip Run A |
| 10 | Peak | 29 | 12 | 5 x 4 min hard | Skip Run C |
| 11 | Taper | 18 | 8 | 10 min tempo | Skip Run A |
| 12 | Taper + race | 9 | Race: 13.1 | 4 strides | Skip Run C |
In week 12, the 9 miles are three short, easy runs. The race is on top of that. Slow the long run down in weeks 9 and 10. You’re practicing endurance, not racing.
What a 4-day week looks like
Here’s peak week 10, which totals 29 miles.
- Tuesday, Run A: 5 miles easy. You could chat the whole way.
- Thursday, Run B: 6 miles with 5 x 4 minutes hard. That’s tough but steady, with 2 minutes of jogging between.
- Saturday, Run C: 6 miles easy. Keep it dull on purpose.
- Sunday, Run D: 12 miles slow.
Hard days feel hard. Easy days feel almost too easy.
Pacing and fueling the long run
Run the long run about a minute per mile slower than your goal race pace. If you can’t tell, go by feel and keep it conversational. Take water along.
Past 75 minutes, practice eating. A common guideline is 30 to 60 grams of carbohydrate per hour, which is roughly one or two gels. Try your race-day fuel on long runs. Your gut learns too.
How fast to build mileage (is the 10% rule real?)
Inside each build block, the plan ramps about 7 to 14% a week. Then it drops back every fourth week.
The jumps after a down week look bigger. Week 5 is 43% above week 4. But it’s only 11% above week 3, the last full build week. Week 9 is 42% above week 8 and 12.5% above week 7. Treat a down week as a pause, not a reset.
Why isn’t the plan stricter? A 2014 study followed 874 novice runners for a year. Those who raised weekly distance by more than 30% over two weeks had more distance-related injuries, such as kneecap pain and patellar tendon trouble. The 10-30% group wasn’t clearly different from the under-10% group. In short: the famous 10% rule is weakly supported, but a giant jump is still a bad idea.
Think of mileage like a credit card limit. You can spend a little more each week. Spend 30% more in a hurry and the bill comes due in your knees.
Steady is faster than fast-then-injured.
80/20: how hard should the hard days be?
Most of your running should feel easy. A common coaching split is about 80% easy and 20% moderate to hard, by time. With four runs, that means one hard day, not two.
A 10-week study of 30 recreational runners compared a polarized plan with a plan stuck between easy and hard. Both groups improved their 10K time. The polarized group improved more. Polarized means mostly easy running with a small dose of truly hard running. Translation: easy days should be easier than you think, and hard days should be clearly hard. Muddy middle days help least.
If you want the full debate, see polarized vs pyramidal training. To learn what “easy” feels like, read how Zone 2 builds the aerobic base.
How 3, 4 and 5-6 run days compare
More days isn’t always better. It’s a trade between time and total volume. These are typical conventions, not study results.
| 3 days (FIRST-style) | 4 days (this plan) | 5-6 days | |
|---|---|---|---|
| Peak weekly miles | 20-25 | 27-30 | 35-45 |
| Long run share of week | About 45% | About 40% | About 30% |
| Run time per week at peak | 3-4 hours | 4-5 hours | 5-7 hours |
| Extra work | 2 cross-training days | Optional strength | Often none |
| Best for | Tight schedules | Most busy adults | Chasing a fast time |
Four days hits the middle. You get enough volume to run 13.1 miles strongly without giving up your evenings.
The 2-week taper: how much to cut
A meta-analysis of tapering found the best results came from a 2-week taper with a 41-60% volume cut. Intensity and frequency stayed the same. In short: run less, but keep the shoes laced and keep a little speed.
Check the math. Weeks 11 and 12 hold 18 and 9 miles before the race. That averages 13.5 miles against a peak of 29. That’s a 53% cut, inside the range. Add the 13.1-mile race to week 12 and the average rises, but the race is the event, not training volume.
What to do when you miss a run, get sick, or travel
Here’s where static plans break. Missed Tuesday, so you cram Tuesday into Wednesday. Now you’re tired for Thursday.
Don’t. Fitness doesn’t vanish in a week. In trained athletes, VO2max (the most oxygen your body can use) fell about 4 to 14% within four weeks of complete rest. That’s four weeks of doing nothing at all. One missed run costs you almost nothing. In short: fitness is a savings account, and a missed run is a coffee, not a mortgage.
A simple rule set:
- Missed a run: skip it. Don’t double up.
- Missed a week: repeat the previous week, then continue.
- Sick with a fever: stop. Restart easy.
- Travel week: keep the long run, shorten the rest.
Check how your body is coping with aerobic decoupling, the drift in heart rate over a steady run. A rising drift ratio means you’re carrying fatigue.
A real-world example
Take a runner named Dana. This is an example, not a client story. She’s 41, works 50 hours a week and has two kids. She ran about 12 miles a week before starting. Her longest run was 4 miles. Her easy pace was 11:30 per mile. She picked Tuesday, Thursday, Saturday and Sunday.
In week 6 she got sick and lost eight days. She wanted to cram. Instead she repeated week 5, then picked up at week 6. That pushed her plan to 13 weeks. She hit her 12-mile long run in week 11 and peaked at 29 miles. Her easy pace dropped to 10:40.
She finished the half marathon in 2:05, about 9:32 per mile. No injuries. Her four days weren’t the secret. Her restraint was.
How AthleteOS keeps the plan alive
Plans fail on the first bad week. AthleteOS builds a half marathon training plan around the four days you choose on your workout calendar. When you miss a run or sleep badly, the AI coach re-slots or drops the session. It protects your long run and your taper. Then it writes a short plain-English note explaining the change. Before race day, the race readiness check tells you whether your fatigue is low and your fitness is where it should be.