How Long Does It Take to Improve Your Half Marathon or Marathon Time?

This is Part 3 of our Getting Faster series. Part 1 covers what actually makes you faster, and Part 2 covers the timeline for new runners. This part is for experienced runners trying to take time off a half marathon or marathon.

In 2018, I ran the Des Moines Marathon in 3:52. In October 2026, at 44, I ran the same course in 3:33.

Here's the strange part. My Garmin VO2 max barely moved during my 19-week training block. It sat around 52 to 54 the whole time. Most days, I didn't feel faster. I felt tired. If I'd judged my progress by my watch or by how my legs felt on a Tuesday, I would have assumed the training wasn't working.

That's what improving looks like once you're past the beginner stage. The gains are smaller, they take longer, and they come from different places than they did when you started. Here's a realistic look at how long it takes, what's actually changing, and how much time you can expect to take off.

Why Experienced Runners Improve Differently

When you're new, almost everything improves quickly, including your VO2 max, the measure of how much oxygen your body can use. Once you've been running for a while, VO2 max tends to level off. It doesn't stop mattering, but it stops being where most of your gains come from.

Exercise physiologists Michael Joyner and Edward Coyle described endurance performance as coming down to three things: VO2 max, threshold (how close to your max you can run before fatigue builds up fast), and running economy (how much energy it takes to run a given pace). For experienced runners, threshold and economy usually have more room to improve than VO2 max.

There's a fourth piece that matters a lot for the half and full marathon: durability. In a 2021 paper in Sports Medicine, Ed Maunder and colleagues, including well-known endurance researcher Stephen Seiler, argued that standard fitness tests miss something important: how well your physiology holds up after hours of running. Two runners with the same lab numbers can race very differently in the last 10K of a marathon, depending on how much they fade.

That's exactly what my numbers showed. My VO2 max went from about 49 to 52–54 during the year I built my mileage from about 20 miles a week to around 30. Then it held steady through my entire marathon block. But my threshold, my economy, my durability over long runs, and my fueling all got better. That's where the 19 minutes came from.

The Timeline for Experienced Runners

Base Building: 3 to 6+ Months

The work that makes a training block successful happens before the block starts. Building and holding a solid weekly mileage is what lets you handle the harder training later.

I held 30 to 35 miles a week for about six months before starting my marathon plan. That's when my VO2 max climbed, and it's what let me handle an average of about 45 miles a week during the block without getting hurt. Our guide to how fast to increase your mileage covers how to build safely.

What's improving: Aerobic fitness, durability, and the ability of your legs to handle more running.

The Training Block: 12 to 20 Weeks

This is where the race-specific work happens: threshold runs, intervals, long runs, and race-pace miles. Mine was 19 weeks.

What's improving: Mostly threshold, running economy, durability, and your ability to hold goal pace late in a race. Not necessarily VO2 max.

What it feels like: Probably not faster. During a hard block, fitness and fatigue build up at the same time, and the fatigue hides the fitness. This idea goes back to a classic training model developed by Eric Banister and colleagues in the 1970s: every workout adds both fitness and fatigue, and fatigue clears faster than fitness. So in the middle of a block, you can be fitter than ever and still feel worn down.

The best way to see your progress mid-block is a tune-up race or a key workout, not your easy runs. Halfway through my block, I ran a 21:58 5K on a hot July day, in the middle of heavy training, with no taper. Plug that into our pace calculator and it's equivalent to roughly a 3:28 marathon. That told me the training was working long before race day. Our article on tune-up races covers how to use them.

The Taper: About 2 Weeks

The taper is where your fitness finally shows up. A 2007 meta-analysis by Laurent Bosquet and colleagues found the most effective taper lasted about two weeks, cut training volume by roughly 41 to 60%, and kept intensity and frequency the same. In other words, run less, but keep some faster running in and don't skip days.

The taper matters for recreational runners, too. In a 2021 study, Barry Smyth and Aonghus Lawlor of University College Dublin analyzed Strava data from more than 158,000 recreational marathoners. Runners who followed a disciplined taper of two to three weeks finished about 2 to 3% faster than expected for their fitness, compared with runners who barely tapered. For a 3:30 marathoner, that's about 4 to 6 minutes from the taper alone.

During my taper, my runs started feeling easy. The weather cooled off, and my heart rate was lower on every run. That's when I knew the block had worked. If your taper feels weird, restless, or flat, that's normal too. Our article on the tapering trap explains why.

Race Day

All of that shows up on race day, as long as you pace it well and fuel it right. Plenty of runners have the fitness for a PR and lose it by going out too fast or falling behind on fueling. Our guide to how to fuel long runs and races covers the fueling side.

Over Multiple Blocks: 1 to 3+ Years

This is where the big improvements come from for most experienced runners. Each block builds on the last. The base you build between blocks gets a little bigger each year. Your durability, economy, and threshold keep creeping up.

But each block usually gives you a little less than the one before. That's diminishing returns, and it's normal. Your first year of structured training might take a huge chunk off your marathon time. Your fifth might take a couple of minutes.

How Much Time Can You Take Off?

There's no single number, but here's how to think about it.

A common guideline: 2 to 3% per training block. You'll often hear that an experienced runner can expect to improve about 2 to 3% from one serious marathon training block, and occasionally as much as 5% when everything comes together. It's a rule of thumb, not a guarantee, but it's a useful way to set expectations. Here's what that looks like:

That's for runners who've already been training seriously. If you're newer to structured training, you may improve more. If you've been chasing PRs for years, you may improve less.

How much room you have matters most. If you've never followed a structured plan, never built real mileage, or have been running your easy days too hard, you probably have a lot of room to improve. If you've been training seriously for years, gains will be smaller.

Fixing mistakes can be worth a lot. A better pacing strategy, a real fueling plan, or slowing down your easy runs can take minutes off a marathon without any change in fitness.

Here's what my numbers looked like over a little more than a year:

*Estimated with our pace calculator. Equivalents are estimates, not guarantees.

From my 2025 half to my 2026 marathon, my marathon equivalent improved from about 3:38 to 3:33. That's about 2.3%, right in that 2 to 3% range.

A few other things worth noticing. My 2025 half was on a tough course, in shoes that gave me giant blisters, so it probably undersold my fitness a little. And my marathon came in a few minutes slower than my mid-block 5K predicted, which is common. Shorter races tend to predict a slightly faster marathon than most runners actually run, because the marathon also tests durability and fueling. If you're curious how watch predictions compare, Garmin predicted 3:35 for me, and I wrote about that in how accurate Garmin's race predictor is.

Set goals from your current fitness, not your hopes. A recent race is the best predictor of what you can run now. If you want a realistic goal, start there. Our article on why your goal pace doesn't drive your training explains why training at your current fitness, not your goal, is what actually gets you there.

What If You're Over 40?

You can still improve. I'm proof. Research by Hirofumi Tanaka and Douglas Seals, published in The Journal of Physiology in 2008, found that endurance performance declines only modestly from your mid-30s into your 50s and 60s before dropping off more steeply. For most masters runners, especially those who haven't trained seriously for long, the room to improve through better training is bigger than the decline from age.

The biggest difference is recovery. You might need more time between hard workouts, more attention to sleep, and more strength training to stay healthy. I wrote about what's worked for me in masters running: how to get faster after 40 and the full story of my race in how I ran a 19-minute marathon PR at 44.

Why You Might Hit a Plateau

If you've stopped improving, it's usually one of these:

• Doing the same thing every block. Your body adapts to what you give it. If your mileage and workouts haven't changed in years, your results probably won't either.
• Running easy days too hard. It's the most common mistake I see. It leaves you too tired to get much out of your hard days. Part 1 of this series covers why most of your running should be easy.
• Training breaks during a block. A 2023 study by Feely and colleagues, also using Strava data, looked at about 290,000 runners and more than 500,000 marathons. Runners who took a break of a week or more from training before race day finished about 5 to 8% slower than they did in their marathons without a break. Life and minor injuries happen, but consistency through a block is worth a lot.
• Inconsistency between blocks. Taking months off after every race means starting over. In a classic 1984 study, Edward Coyle and colleagues found trained endurance athletes lost a noticeable amount of VO2 max within the first few weeks of stopping training, and the decline kept going for a couple of months before leveling off. A recovery break after a race is good. Just don't let it turn into a whole season off. Our guide to post-race recovery covers getting back safely.
• Injuries. Nothing slows progress like weeks off with an injury. Building gradually and strength training are your best protection.
• Not enough recovery. More training doesn't help if you can't recover from it.

Signs Your Training Is Working (Even If You Don't Feel It)

During a block, watch for these instead of how you feel on easy days:

• You're hitting your workouts, or they feel a little more controlled than they did a month ago
• Your heart rate is lower at the same pace, especially once the weather cools off
• Your long runs feel more manageable late in the run, a sign of better durability
• A tune-up race comes in faster than your last one at that distance
• You recover from long runs faster than earlier in the block

FAQ

How much can I improve my marathon time in 16 weeks? A common guideline for experienced runners is about 2 to 3% from one serious training block, and occasionally up to 5%. For a 3:30 marathoner, that's roughly 4 to 6 minutes, or about 10 minutes in a great block. Runners newer to structured training can often improve more. A recent race is the best way to set a realistic goal.

How long does it take to improve a half marathon time? A focused 10- to 16-week training block, built on a solid base, is enough to see real improvement for most experienced runners. Bigger improvements usually come over several training cycles.

Why isn't my VO2 max going up even though I'm getting faster? For experienced runners, VO2 max often levels off. Most later improvement comes from better threshold, running economy, and durability, which your watch's VO2 max number doesn't fully capture. Mine stayed around 52 to 54 during the block that got me a 19-minute marathon PR.

Why don't I feel faster during marathon training? Fatigue from training hides your fitness. Most runners feel tired during a hard block and only feel the improvement once they taper.

How long should a marathon taper be? Research suggests about two weeks works best, cutting training volume by roughly 40 to 60% while keeping some faster running and your usual number of running days.

Can you still get faster after 40? Yes. Endurance performance declines only modestly through your 40s and 50s, and better training can more than make up for it. I ran my marathon PR at 44.

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This article is for general information and isn't medical advice. If you have an injury or a medical condition, talk to your doctor or a physical therapist before changing your training.

Sources

• Joyner, M. J., & Coyle, E. F. (2008). Endurance exercise performance: the physiology of champions. The Journal of Physiology, 586(1), 35–44.
• Maunder, E., Seiler, S., Mildenhall, M. J., Kilding, A. E., & Plews, D. J. (2021). The importance of "durability" in the physiological profiling of endurance athletes. Sports Medicine, 51, 1619–1628.
• Calvert, T. W., Banister, E. W., Savage, M. V., & Bach, T. (1976). A systems model of the effects of training on physical performance. IEEE Transactions on Systems, Man, and Cybernetics, 6(2), 94–102.
• Bosquet, L., Montpetit, J., Arvisais, D., & Mujika, I. (2007). Effects of tapering on performance: a meta-analysis. Medicine and Science in Sports and Exercise, 39(8), 1358–1365.
• Smyth, B., & Lawlor, A. (2021). Longer disciplined tapers improve marathon performance for recreational runners. Frontiers in Sports and Active Living, 3.
• Feely, C., Smyth, B., Caulfield, B., & Lawlor, A. (2023). Estimating the cost of training disruptions on marathon performance. Frontiers in Sports and Active Living, 4.
• Tanaka, H., & Seals, D. R. (2008). Endurance exercise performance in Masters athletes: age-associated changes and underlying physiological mechanisms. The Journal of Physiology, 586(1), 55–63.
• Coyle, E. F., Martin, W. H., Sinacore, D. R., Joyner, M. J., Hagberg, J. M., & Holloszy, J. O. (1984). Time course of loss of adaptations after stopping prolonged intense endurance training. Journal of Applied Physiology, 57(6), 1857–1864.

Ready to see what you can run now? Our free training plan builder sets your paces from your current fitness and builds your block from there.