Training Half Marathon Long Runs by Time Not Miles

Your plan is written in miles, but at your pace those mile targets translate into hours on feet that don't match anyone else's experience of the same plan. If you're training by time rather than distance, cap your longest training session at 2.5-3 hours on feet, regardless of how many miles that covers. Beyond 3 hours, injury and recovery-cost risk rises faster than fitness benefit — this replaces "run further" with "run this long, well." Most training plans are written in miles because that's easy to publish, not because it's the right metric for every runner. If your easy pace is 11 minutes a mile or slower, converting to time makes the plan actually usable. Here's how.

Stay locked to the mileage number instead, and you end up either chasing distance well past your body's real recovery capacity, or cutting a session short and quietly telling yourself you "didn't finish" a run you actually completed in full. Neither does you any good. Once you're training by the clock instead of the odometer, that math stops working against you.

Converting Your Plan: Turning Mileage Targets Into Time Targets

Most half marathon plans are written in miles, and that's fine if your pace matches the assumptions baked into the plan. It stops being fine the moment your pace is meaningfully slower than the plan's author had in mind. An 8-mile long run sounds identical on paper for a 9-minute miler and a 14-minute miler, but it's a completely different session in terms of time on feet.

The fix is a simple conversion: take the mileage-based plan's weekly long run distance and multiply it by your own current easy/long-run pace — not a faster, aspirational pace. An 8-mile long run at a 13:30/mile easy pace becomes a 108-minute time target. Round to the nearest 10-15 minutes and use that as your session length, regardless of the exact distance you end up covering.

This is the exact formula I use to translate a mileage-based plan into a personalised time target for slower-paced athletes. It's not a rough guess — it's the same weekly progression the plan intends, just measured in the unit that actually matters for your training stress.

Progressing Your Long Run Duration Week to Week

Once you've converted your starting point into minutes, progress it the same way a mileage plan would progress distance. Apply roughly a 10% increase per week, with a cutback every third or fourth week. The only change is the unit — minutes instead of miles.

In practice that looks like 90 minutes, then 100, then 110, then a cutback week down to 80 minutes before building again. You never need to know the exact distance covered in any of these sessions. Track minutes on feet, not the number on your watch's distance field, and the progression takes care of itself.

Run-Walk Ratios and Pacing by Effort, Not Pace-Per-Mile

If you're using run-walk intervals, nothing changes when you switch to training by time. A 4-minute run/1-minute walk ratio still applies for the full time-on-feet target you've set, whether that's 90 minutes or 2.5 hours. The ratio is the constant — the clock decides when the session ends, not a distance marker.

Judge whether the ratio is right by perceived effort rather than a per-mile pace number, since pace-per-mile isn't the metric you're tracking anymore. You should be able to speak in full sentences throughout. If you can't, the ratio or the pace within it needs adjusting.

I've noticed a consistent pattern here over the years: athletes who abandon their run-walk ratio "because they're not tracking miles anyway" show worse late-run form and higher perceived effort than those who hold the ratio regardless of the metric being tracked. The ratio isn't just about pace — it's about managing fatigue across the whole session.

How Long Is Long Enough: The 2.5-3 Hour Ceiling in Practice

For most half marathon goal times over roughly 2:30-2:45, the race itself may take close to or beyond your training long-run time ceiling. That's fine, and it's expected. The long run's purpose is building time-on-feet tolerance and fuelling practice — it is not a literal rehearsal of the full race distance.

I cap every athlete's long run at 3 hours regardless of pace. Beyond that point I'm managing injury risk, not building fitness, and the trade-off stops being worth it. Trust the ceiling even if it means your longest training run finishes before your goal race would.

Using Heart Rate and RPE to Self-Pace Without a Distance Target

Keep long run effort at RPE 3-4 out of 10, or a heart rate zone corresponding to roughly 65-75% of max, checked periodically rather than continuously. The whole point of training by time is training by feel and duration, not by numbers scrolling past on a screen.

Glancing at heart rate every 10-15 minutes is plenty. Constantly monitoring it defeats the purpose of stepping away from distance-obsessed training in the first place, and it tends to make runners chase numbers instead of listening to their body.

Adjusting Time-Based Long Runs as Race Day Approaches

Your peak time-on-feet session should land 2-3 weeks before race day, exactly as it would in a mileage-based build. From there, taper duration by roughly 25-40% in the final two weeks — the same proportion a mileage-based plan would cut from its longest run.

This keeps the taper logic identical across both approaches. Only the unit of measurement differs.

Treadmill and Track Options When Outdoor Time Is Limited

A treadmill session at 1% incline works identically for time-based training. Set the display to time remaining rather than distance, and use run-walk interval timers — many treadmills support these natively — rather than manually tracking your ratio on top of everything else.

This removes the temptation to watch the distance counter creep up too slowly, which is precisely the mental trap time-based training is designed to avoid.

Frequently Asked Questions

How do I convert a mileage-based long run plan to a time-based one?

Take the distance the plan prescribes and multiply it by your own current easy/long-run pace, not a faster aspirational pace. An 8-mile long run at a 13:30/mile easy pace becomes a 108-minute time target. Round to the nearest 10-15 minutes and train to that duration regardless of the exact distance it covers.

What's a safe maximum time on feet for a half marathon long run if I'm training by time?

Cap your longest training session at 2.5-3 hours on feet, regardless of how many miles that covers. Beyond 3 hours, injury and recovery-cost risk rises faster than fitness benefit, so this replaces "run further" with "run this long, well."

Do run-walk intervals change if I'm training by time instead of miles?

No. A 4-minute run/1-minute walk ratio still applies for the full time-on-feet target regardless of how you're measuring the session. Judge whether the ratio is right by perceived effort — you should be able to speak in full sentences throughout — rather than by a per-mile pace number.

How do I know if I'm running too fast without tracking miles?

Use perceived effort and, if you have one, a heart rate monitor. Long run effort should sit at RPE 3-4 out of 10, or a heart rate zone of roughly 65-75% of max, checked periodically rather than continuously. If you can't hold a conversation, you're running too fast for this session.

How do I use heart rate or RPE to pace a long run without a distance target?

Keep effort at RPE 3-4/10 or 65-75% of max heart rate, checking in every 10-15 minutes rather than staring at the screen continuously. The point of training by time is training by feel — leaning on the numbers too heavily defeats the purpose.

What's the minimum long run duration to finish a half marathon comfortably?

Most runners training by time should build toward at least 2-2.5 hours on feet at some point in the build, ideally 2-3 weeks before race day. This builds the fuelling and time-on-feet tolerance the race itself will demand, even if your race finish time is longer than your longest training session.

How does time-based long run training change as race day gets closer?

Your peak time-on-feet session should land 2-3 weeks before race day. From there, taper duration by roughly 25-40% over the final two weeks, exactly as a mileage-based plan would taper distance.

Can I still do fast-finish or progression long runs while training by time?

Yes. Keep the same structure — an easy majority of the session followed by a faster final segment — but define both portions in minutes rather than miles. For example, 90 minutes easy followed by 20 minutes at a stronger effort, rather than a mile-based breakdown.

How do I do treadmill long runs without a distance target?

Set the treadmill to 1% incline and switch the display to time remaining rather than distance. Many treadmills support native run-walk interval timers, so use those instead of manually tracking your ratio on top of everything else.

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