Picking a marathon training plan is one of the most important decisions you will make in the months before race day. Pick one that is too easy and you leave fitness on the table. Pick one that is too hard and you risk injury, burnout, or showing up to the start line already depleted.
The Pfitzinger marathon plans sit in a category of their own. They are structured, science-backed, and demanding in a way that produces real results when the runner is ready for them. The two most popular options the 18/55 and the 18/70 are built on the same philosophy but represent meaningfully different workloads.
If you are trying to figure out which one belongs in your training cycle, this article breaks both plans down clearly, compares them directly, and helps you make the right call for where you are right now.
What Is the Pfitzinger Marathon Training Plan?
The Pfitzinger marathon plans come from the book Advanced Marathoning, co-authored by Pete Pfitzinger and Scott Douglas. First published in 2001 and updated in subsequent editions, the book is widely regarded as one of the most thorough and evidence-based marathon training resources available to non-elite runners.
The plans inside the book are designed for runners who already have a base of aerobic fitness and are ready to train seriously. They are not beginner programs. They prioritize running volume, aerobic development, lactate threshold work, and race-specific preparation — in a way that mirrors how elite athletes approach marathon training at a scaled-down level.
Two plans in particular have become the most widely used by competitive age-group runners and marathon enthusiasts: the 18/55 and the 18/70. Both run for 18 weeks. The number after the slash refers to the peak mileage week within the plan.
Who Is Pete Pfitzinger?
Pete Pfitzinger is an American distance runner and exercise physiologist. He competed in the 1984 and 1988 Olympic Games as a marathoner, finishing eighth in the 1984 Los Angeles Olympics. After his competitive career, he worked as a coach and performance science director and co-authored Advanced Marathoning along with Scott Douglas.
His training philosophy is rooted in exercise physiology research. The plans he designed reflect how the aerobic system responds to training stress — including how mileage, recovery, and workout quality interact over a long training block. That scientific foundation is a large part of why his plans remain respected decades after they were first published.
Understanding the Plan Naming System
The naming format used for Pfitzinger plans is simple once you understand it. The first number always refers to the length of the training plan in weeks. The second number refers to the highest weekly mileage you will reach at any point during the plan.
So the Pfitz 18/55 plan runs for 18 weeks with a peak week of 55 miles. The Pfitz 18/70 plan also runs for 18 weeks, but the peak week reaches 70 miles. This distinction matters more than it might appear, because the entire training structure how long your long runs are, how many miles of tempo and lactate threshold work you log, how much recovery is built in scales with that mileage ceiling.
There is also a Pfitz 12/55 plan for runners with less lead time, and higher-mileage options in the book for those targeting elite performance. For most serious recreational runners, the 18/55 and 18/70 are the two realistic options.
Pfitz 18/55 at a Glance
Weekly Mileage Structure
The 18/55 plan builds from a starting base of around 35 to 40 miles per week and peaks at 55 miles during the highest-demand weeks of the training block. The progression is gradual by design. Mileage builds over several weeks, pulls back briefly for recovery, then builds again before a taper in the final two to three weeks before race day.
Most runners following this plan will run five to six days per week. Rest days are structured and not optional. The plan treats recovery as part of the training load, not as a reward for hard work.
Key Workouts
The 18/55 plan includes the full range of Pfitzinger workout types. Lactate threshold runs — typically run at a comfortably hard effort for 20 to 40 minutes appear regularly and form the core of speed development within the plan. Medium-long runs in the 13 to 16 mile range appear midweek to build aerobic endurance between weekend long runs. Long runs reach up to 22 to 23 miles at the peak of the plan.
VO2 max intervals and marathon-pace segments are also included, though less frequently than in the 18/70. The balance leans toward building a strong aerobic base over accumulating high-intensity volume.
Who It Is Built For
The 18/55 is designed for runners who are consistently logging 35 to 40 miles per week before starting the plan. If your current training sits below that range, the jump in mileage during the first few weeks will feel abrupt and carries an injury risk.
It is also well-suited for runners who have completed marathon training before but have not yet trained at the Pfitzinger level, and for experienced runners returning after a gap or managing a history of injury. The 18/55 is serious training it is not light mileage by any standard but it sits within a range that a well-prepared recreational runner can handle.
Pfitz 18/70 at a Glance
Weekly Mileage Structure
The 18/70 plan builds from a starting base closer to 45 to 55 miles per week and peaks at 70 miles. For runners who are already accustomed to that kind of volume, the build feels manageable. For runners who are not, it will be too much too fast.
The structure follows the same weekly rhythm as the 18/55 easy days, medium-long runs midweek, long runs on the weekend but every component is scaled up. More total miles means more aerobic stress and, when managed correctly, more aerobic adaptation.
Key Workouts
At the 18/70 level, the plan includes all the same workout types but with greater frequency and slightly longer durations. Lactate threshold runs are longer. Medium-long runs push further into the 15 to 17 mile range. Long runs can reach 23 to 24 miles at the peak of the block.
The additional mileage in the 18/70 comes primarily from the easy and medium-effort days. More miles at controlled effort builds the aerobic engine without dramatically increasing injury risk, provided the runner enters the plan with an appropriate base.
Who It Is Built For
The 18/70 is designed for experienced marathoners who already train at 50 or more miles per week consistently. If 70-mile weeks feel familiar in context not as a personal record, but as something within reach from your current training the plan is an appropriate challenge.
This plan suits runners who have completed a Pfitzinger plan before and handled the 18/55 well, or runners with a strong endurance background who are chasing a personal best and know their body responds to volume.
Pfitz 18/55 vs 18/70: The Core Differences
| Feature | Pfitz 18/55 | Pfitz 18/70 |
|---|---|---|
| Plan Length | 18 weeks | 18 weeks |
| Peak Weekly Mileage | 55 miles | 70 miles |
| Recommended Starting Base | 35–40 miles per week | 45–55 miles per week |
| Peak Long Run | 22–23 miles | 23–24 miles |
| Midweek Medium-Long Run | 13–16 miles | 15–17 miles |
| Days Per Week | 5–6 days | 6–7 days |
| Best Fit | Serious recreational runners new to Pfitzinger or returning after a gap | Experienced marathoners with consistent high mileage and a prior Pfitz cycle |
The most visible difference is the mileage ceiling: 55 miles versus 70 miles. But the practical impact goes beyond that one number. Higher peak mileage means higher average weekly mileage throughout the block, which means more cumulative fatigue, more recovery demand, and more required consistency over the full 18 weeks.
Both plans use the same training principles and the same workout types. The difference is volume and the aerobic stress that comes with it. The 18/70 asks more of the runner across every dimension — longer long runs, longer midweek runs, and more total miles on the easy days that fill in around the quality sessions.
Neither plan is objectively better. The better plan is the one that matches where you are right now.
How to Choose Between the Two Plans
Your Current Weekly Mileage
This is the most reliable filter. If you are not currently running the mileage that the plan starts with, do not start that plan yet.
The 18/55 typically opens in the 35 to 40 mile range. The 18/70 opens closer to 45 to 55. If your current base is below the opening weeks of a plan, you will spend the early weeks digging a hole rather than building fitness and you may not recover from that hole before race day.
If you are sitting at 30 to 35 miles per week, spend six to eight weeks building your base before beginning the 18/55. Do not rush the entry point.
Your Training History
Mileage history matters as much as current mileage. A runner who has averaged 45 miles per week for the past year is in a very different position than a runner who recently ramped to 45 miles over the past three weeks. The body adapts to training load over time. Bone density, tendon strength, and aerobic capacity all develop gradually.
If you have trained consistently at higher mileage for at least one full training cycle, the 18/70 is a reasonable step. If you are newer to structured training or returning after a break, the 18/55 is the smarter foundation.
Your Goal for Race Day
Both plans produce meaningful fitness gains when executed correctly. The 18/55 is not a consolation prize — it is what a serious, well-prepared recreational runner needs to race well.
The 18/70 offers a potential edge for runners who are already near the top of their fitness ceiling and need more volume to push their performance forward. If you have already done the 18/55 and executed it cleanly, moving to the 18/70 for your next cycle is a logical progression.
If your goal is to finish strong, qualify for Boston, or set a personal best at your current fitness level — the 18/55 done well will serve that goal better than the 18/70 done poorly.
Your Schedule and Recovery Capacity
Higher mileage requires more sleep, more nutrition, and more recovery time outside of running. Life stress and training stress are not separate systems in the body. A demanding job, disrupted sleep, or significant life demands will reduce your capacity to absorb a 70-mile training week.
Be honest about what your schedule actually allows. A completed 18/55 cycle will always produce better results than an abandoned or injury-shortened 18/70 cycle.
What Runners Get Wrong When Choosing a Pfitz Plan
The most common mistake is choosing a plan based on ambition rather than readiness. Runners who want to run a fast marathon sometimes assume that more mileage automatically means better results. That logic only holds when the runner is actually prepared to absorb and recover from that mileage.
The second mistake is ignoring the base phase. Both Pfitzinger plans assume you enter week one with a solid aerobic base already in place. If you are building from scratch or returning from an injury, add a base-building phase before starting the 18-week block. Pfitzinger addresses this in Advanced Marathoning directly — the 18-week plan is not the starting point, it is the final preparation phase.
A third mistake is treating the easy days as optional or interchangeable. Easy runs in a Pfitzinger plan are not filler. They carry aerobic training load that accumulates over weeks and contributes directly to your fitness at peak mileage. Skipping them to add rest undercuts the plan’s design.
A Note on the Pfitzinger 12-Week Marathon Plan
For runners who sign up for a marathon with less lead time, Advanced Marathoning includes a 12-week plan that peaks at 55 miles per week. This is sometimes searched for as the Pfitz 12/55.
The 12-week plan covers the same workout types but compresses the build and includes less time to develop aerobic fitness before the quality work begins. It is best suited for runners who are already in strong aerobic shape and simply need a structured final preparation phase rather than a full training build.
If you have the time, the 18-week format will serve you better for most race goals.
What to Expect During an 18-Week Pfitzinger Block
The first four to six weeks will feel manageable but accumulative. Fatigue builds gradually. Most runners feel strong early and underestimate how that changes.
Weeks seven through twelve represent the highest-demand period of the plan. Mileage is peaking, workouts are at their most demanding, and recovery starts to matter more. This is the stretch where sleep quality, nutrition, and patience make the biggest difference.
The taper typically the final two to three weeks involves a meaningful reduction in mileage while key workout quality is maintained. Many runners feel worse during the taper than they expected. Tired legs, brief illness, and general restlessness are all common and not cause for concern. Trust the structure.
On race day, the investment of 18 weeks typically shows in the second half of the marathon — the part where underprepared runners slow down and well-prepared runners hold pace.
Final Verdict
The Pfitzinger marathon plans are among the most effective structured training programs available to serious recreational runners. Both the 18/55 and the 18/70 are built on sound exercise physiology and have delivered results for thousands of runners over many years.
The right choice between them is not about which plan looks more impressive. It is about which plan matches your current mileage base, your training history, your schedule, and your recovery capacity. Choose the 18/55 if your base sits comfortably in the 35 to 40 mile range. Move to the 18/70 when you have a completed Pfitzinger cycle behind you, consistent higher mileage in your legs, and the lifestyle capacity to absorb a 70-mile peak week.
Either plan, executed honestly and consistently, will prepare you to run your best marathon.
