What is a long run, and how long should yours be?

What makes a run a long run

The long run is simply the longest run in your week. It's run at an easy to steady effort — in Taper's words, “time on feet is the goal” — so you should be able to chat in full sentences for most of it. If you're gasping, you're going too fast.

It's the session that builds your endurance. It teaches your body to keep going for hours and to burn fat for fuel, it strengthens tendons and muscles that shorter runs don't reach, and it's where you practise drinking and eating exactly as you will on race day. For marathon training it's the single most important run of the week.

What it isn't: a race, a time trial, or a chance to prove anything. Save the harder breathing for tempo runs and intervals.

How long should my long run be?

There's no single number that suits everyone — it depends on what you're training for, how much you're already running, and how much time you realistically have. The most useful way to answer it is in time, not distance.

• Getting started, or training for a first 5 km (3.1 miles): 30–45 minutes is plenty, even if you walk parts of it.
• Training for a 10 km (6.2 miles): build towards about 60 minutes.
• Training for a half marathon (21.1 km / 13.1 miles): build towards 90 minutes, with the longest runs around 2 hours at the top end.
• Training for a marathon (42.2 km / 26.2 miles): long runs usually build to about 2.5–3 hours. Many coaches stop at three hours, because past that the recovery cost tends to outweigh the extra benefit.

Notice that none of those require running the full race distance in training. Marathon runners rarely go beyond about 32 km (20 miles) before race day, and plenty go less. The race itself — with fresh-ish legs and proper fuelling — is where the full distance happens.

Build up gently: add a few minutes at a time rather than jumping, and every third or fourth week keep the long run shorter so the work settles in. A long run that leaves you unable to run for two days was too long.

Why time beats distance

Distances lie a little. The same 15 km (9.3 miles) is a very different run on a flat towpath, a hilly trail or a hot afternoon — and if you're a slower runner, a distance-based plan quietly asks more of you than it does of someone else. Time keeps the effort honest.

If you do want a distance target, pick a route you know and keep the effort easy throughout. How slow should easy runs be? goes into the pace question properly.

Fitting it into your week

One long run a week is plenty for most people. Give it a day when you're not rushed, and keep the day after it easy or completely off — that's when the adaptation actually happens. The NHS suggests adults aim for at least 150 minutes of moderate activity a week, and easy running counts towards that.

The long run is also where fuelling matters most. Anything over about 75 minutes is worth practising gels or chews on, starting early rather than waiting until you feel empty. What to eat before a run covers before, during and after.

Wondering how many weeks the whole build takes? How long to train for a marathon has the timeline, and what is tapering before a marathon? explains why your long runs shrink on purpose in the final weeks.