How to pace a marathon

The opening kilometres of a marathon will feel easy, and that is exactly why they are dangerous. A simple plan made before race day protects the part of the race that decides your time.

The easy start is a trap

On race morning you are rested from the taper, full of carbohydrate and surrounded by thousands of excited runners. Adrenaline dulls your sense of effort, so goal pace feels almost lazy. Running 10 seconds per kilometre faster seems harmless.

It is not. The price for a fast start is not paid at 5 km, when you feel great. It is paid after 30 km, when you no longer have the reserves you spent early. Most runners who "hit the wall" did not run out of fitness. They ran out of patience in the first hour.

What a fast start costs

• Fuel. Carbohydrate use rises steeply with pace. A few seconds per kilometre too fast drains your glycogen stores noticeably sooner.
• Heart rate. Heart rate creeps upward through any long race as you warm up and lose fluid. Start higher and you reach your ceiling earlier.
• Legs. Faster running means harder landings. Over more than 20,000 strides, the extra load shows up as heavy, slow legs in the final 10 km.
• Head. If the effort feels hard before halfway, the last third becomes about survival rather than racing, and decisions about pace and fuel get worse.

Studies of large city marathons show the same pattern again and again: most recreational runners slow down clearly in the second half, while the fastest and most experienced runners run close to even splits. Even pacing is a skill, and it can be learned.

Set an honest target

Base your goal on a recent half marathon or 10K, not on hope. The race time predictor turns that result into a marathon estimate. Then adjust for the day: heat, hills, wind or a training block with interruptions all point to the slower end. The heat adjustment calculator shows how much to slow down when it is warm.

Run the race in three parts

0–10 km: settle. Run at goal pace or up to 5 seconds per kilometre slower. It will feel too easy. That is correct. Holding back 5 seconds per kilometre for the first 5 km costs you only 25 seconds.

10–30 km: cruise. Lock into goal pace and stay there. Effort rises slowly, which is normal. Keep fuelling on schedule even when you do not feel you need it.

30 km to the finish: race. This is where your time is decided. If you started patiently, you can hold pace here or push slightly. Speeding up over the last 5 km does not mean you started too slowly. It means you paced it right.

Race-day habits that help

• Trust average pace, not instant pace. GPS pace jumps around with every bend and building. Use lap or average pace, or a pace band with split times every 5 km.
• Let effort overrule the watch. The same pace into a headwind on a warm day costs far more than on a cool, calm morning. If it feels harder than planned, slow down.
• Plan your drinks and gels. Decide in advance which stations you will use and what you will take, and practise it in long runs. A few seconds at an aid station saves minutes later.
• Run your own race. The runner beside you has a different goal, fitness and fuel plan. Follow a pacer only if their target is yours and they run even splits.
• Take sensible lines. Courses are measured on the shortest route. Cut corners where it is safe, but do not zig-zag for seconds.

The short version

Nobody remembers how fresh they felt at 5 km. Everyone remembers how they felt at 35 km. Start slower than you want, hold steady through the middle and save your racing for the final 12 km.

Common questions

How much slower should I start a marathon?

Run the first 5 km at goal pace or up to 5 seconds per kilometre slower. It costs you less than half a minute and protects the last 12 km.

Is a negative split better than even pacing?

Aim for even pacing with the option to speed up slightly after 30 km. A small negative split is a sign of good pacing, not a target to force.

Should I follow a pacer?

Only if the pacer's goal is yours and they run even splits. Stay close but run your own effort.